FDM printing has a vocabulary that makes sense once you understand the physics but is genuinely confusing when you encounter it cold. This glossary covers the 40 terms you’ll see most in guides, forums, slicer menus, and printer documentation, with plain-language definitions that explain not just what each term means but why it matters.
A
AMS (Automatic Material System). Bambu Lab’s multi-spool filament management system. Stores 4 spools, switches filament automatically during multi-color prints, detects runout, and monitors feed tension. The AMS Lite (A-series printers) and AMS 2 Pro (P and H-series) are different hardware with the same general function.
Anisotropic. Having different properties in different directions. FDM prints are anisotropic: stronger in X and Y (along layers) than in Z (through layers). Contrast with isotropic (same properties in all directions), which SLS nylon parts approach.
ASA (Acrylonitrile Styrene Acrylate). A weather-resistant FDM filament similar to ABS but with superior UV resistance. The correct material for outdoor permanent installations in Florida sun.
B
Bed adhesion. How well the first layer sticks to the build plate. Affected by build plate cleanliness, z-offset, bed temperature, and first layer settings. Loss of bed adhesion is the most common cause of print failure.
Brim. A flat, single-layer ring of material printed around the base of a model to increase the first-layer footprint. Improves bed adhesion and reduces warping. Removed after printing. Contrast with Raft (a full platform under the model) and Skirt (doesn’t touch the model).
Bowden setup. An extruder configuration where the extruder motor sits on the printer frame and pushes filament through a long PTFE tube to a lightweight hotend. Allows a lighter printhead (faster speeds) but causes issues with flexible filaments and introduces slight lag. Contrast with direct drive.
Bridge / Bridging. Printing a horizontal span of filament between two support points with no material below. FDM can bridge clean spans up to about 50-60mm at correct settings. Beyond that, sag or collapse occurs.
C
Cold pull. A nozzle cleaning technique. Filament is pushed through at printing temperature, cooled to ~90°C (glass transition), then pulled out firmly. The pulled filament carries debris from the nozzle bore. Repeated until clean. Most effective preventive maintenance for partial clogs.
Combing. A slicer setting that keeps the nozzle over solid printed material during travel moves rather than crossing open air. Reduces stringing by eliminating travel moves where ooze would deposit between printed sections.
Cura. A popular open-source slicer developed by Ultimaker. One of the three most widely used slicers alongside Bambu Studio and PrusaSlicer/Orca Slicer.
D – E
Direct drive. An extruder configuration where the motor sits directly on the printhead, adjacent to the hotend. The filament path from drive gear to nozzle is 2-3cm. Better for flexible filaments and higher retraction precision. Adds weight to the printhead. All Bambu Lab printers use direct drive.
Elephant’s foot. A slight outward flare at the base of a print where the first layer is wider than designed. Caused by z-offset too low (too much first layer squish) combined with high bed temperature.
Extrusion multiplier / Flow rate. A scaling factor that increases or decreases the amount of filament the slicer commands the extruder to push. A flow rate of 1.0 (100%) means the slicer’s calculated volume. Tuning flow rate compensates for filament diameter inconsistency or extruder calibration error.
F – G
FDM (Fused Deposition Modeling). The 3D printing process that melts thermoplastic filament and deposits it layer by layer. The most common and accessible form of consumer 3D printing. Also called FFF (Fused Filament Fabrication), the term preferred in open-source communities.
Flow dynamics calibration. Bambu Lab’s name for their pressure advance calibration routine. Prints a test pattern and measures the result to set an optimal pressure advance value per filament profile.
G-code. The machine instruction language FDM printers run. Contains every movement, temperature change, and extrusion command for a print. Produced by the slicer from the STL file and your settings. Full explanation at the G-code guide.
Gyroid. An infill pattern based on a triply periodic minimal surface. Provides equal strength in all three axes, prints smoothly at high speeds, and is the recommended default infill for most FDM applications.
H – L
Heat creep. A condition where heat travels up from the hotend into the cold zone of the heatbreak, partially melting filament before it reaches the nozzle. Causes soft jams, inconsistent extrusion, and clicking from the extruder. Often caused by inadequate cooling of the heatsink or running at excessively high temperatures for extended periods.
Heatbreak. The thin-walled tube that connects the heat block (hot zone) to the heatsink (cold zone). Designed to create a sharp thermal transition. Critical for preventing heat creep.
Infill. The internal structure of a 3D print. The pattern and density are set in the slicer. Serves to support top surface layers and add structural strength. Usually 10-20% for hobby prints. Full guide at the infill guide.
Input shaping. A firmware technique that compensates for printer resonance frequencies to allow high-speed printing without ringing artifacts. Bambu Lab implements this as part of their vibration compensation calibration.
Layer adhesion. The strength of the bond between adjacent layers. Affected by temperature, speed, cooling, and layer height. FDM parts always fail most easily between layers (Z-direction) rather than along layers.
Layer height. The thickness of each printed layer in millimeters. Determines print resolution (lower = finer detail) and print time (lower = slower). Must not exceed 75% of nozzle diameter. Full guide at the layer height guide.
Lightning infill. A minimal infill pattern that generates only enough structure to support top surface layers, shaped like tree branches growing inward from the walls. Very fast and light; provides no meaningful structural strength.
M – P
Manifold. A mesh where every edge is shared by exactly two faces, with no holes or non-manifold edges. A manifold (water-tight) mesh is required for reliable slicing. Non-manifold meshes produce slicer errors or missing walls.
Melt zone. The region inside the nozzle where filament transitions from solid to liquid. The size and temperature of the melt zone affects flow rate consistency and retraction behavior.
Over-extrusion. Depositing more filament than the slicer intended. Causes rough surfaces, blobs, and dimensional inaccuracy. Usually caused by flow rate too high, temperature too high, or speed too low.
Overhang. A feature of a model that extends outward beyond the material below it. Overhangs under 45 degrees from vertical are self-supporting in FDM. Steeper overhangs require supports or design mitigation.
PEI (Polyetherimide). The surface material used on most modern FDM build plates. Provides excellent adhesion when hot and releases prints cleanly when cooled. Available in smooth and textured variants.
Pressure advance. A firmware correction that compensates for the lag between extruder motion and actual filament flow at the nozzle. Reduces corner blobs and line-start under-extrusion at high speeds.
R – S
Retraction. The reverse movement of the extruder motor to pull filament back into the nozzle before a travel move. Reduces stringing by removing pressure from the melt zone during non-printing moves.
Ringing (Ghosting). A rippled pattern on print surfaces near sharp corners, caused by mechanical vibration resonance after fast direction changes. Addressed by input shaping / vibration compensation calibration.
Seam. The point on each printed layer where the perimeter loop starts and ends. Visible as a small mark on the exterior of prints. Slicers try to place seams at concave angles or user-specified locations to minimize visibility.
Shore hardness. A measurement of material hardness. Used to characterize TPU flexibility. Shore 95A is moderately flexible (shoe-sole feel). Shore 83A is soft and rubbery.
Slicer. Software that converts a 3D model (STL, 3MF) into G-code printer instructions. Applies settings for layer height, temperature, speed, infill, supports, and all other print parameters. Common slicers: Bambu Studio, Orca Slicer, PrusaSlicer, Cura.
Spaghetti. The informal term for a catastrophic mid-print failure where the detached print is dragged by the nozzle, depositing tangled strings of filament in a pile. Named for the obvious visual resemblance.
Stringing. Thin filament strands between printed sections, created during travel moves when residual pressure in the melt zone oozes filament. Reduced by retraction tuning, combing, and temperature adjustment.
Supports. Temporary structures generated by the slicer to support overhanging features during printing. Removed after the print is complete. Well-designed FDM models avoid supports through deliberate geometry choices.
T – Z
TPU (Thermoplastic Polyurethane). A flexible FDM filament that remains elastic at room temperature. Used for straps, gaskets, flexible joints, and impact-absorbing parts. Requires direct drive extruder for reliable printing.
Under-extrusion. Depositing less filament than the slicer intended. Causes gaps in walls, rough surfaces, and weak layer adhesion. Common causes: partial clog, temperature too low, print speed too high, or wet filament.
Vase mode (Spiralize). A slicer mode that converts a model to a single continuous spiral rather than discrete layers, eliminating the seam and producing a smoother exterior surface. Requires specific model geometry. Full guide at the vase mode guide.
Walls (Perimeters / Shell). The outer surface lines of an FDM print. Wall count is the primary structural variable: more walls mean a stronger, heavier part. Three to four walls are standard for functional parts. Two walls are adequate for display-only prints.
Warping. Curling or lifting of a print at the corners or edges as the material cools and contracts unevenly. More common with ABS and ASA than PLA. Addressed by bed temperature, enclosure, brim, and draft elimination. Florida AC drafts are a specific warping cause for open-frame printers near vents.
Z-hop. A brief upward movement of the Z-axis before travel moves to lift the nozzle clear of the print surface and avoid dragging across printed features. Reduces surface marks during travel but adds small amounts of time per travel move.
Z-offset. The calibrated gap between the nozzle tip and the build plate at the start of the first layer. Correct z-offset produces first layer lines that are slightly squished into the surface. Too high: spaghetti on the bed. Too low: nozzle scrapes the surface.