GLOSSARY
FDM (Fused Deposition Modeling)
FDM is the 3D printing process where a heated nozzle extrudes molten plastic filament in thin layers that fuse to each other. It is what most people mean when they say '3D printer'.
Definition
FDM was patented by Scott Crump, co-founder of Stratasys, in 1989. A roll of plastic filament (PLA, PETG, ABS, etc.) feeds into a heated extruder; the extruder melts the plastic and deposits it on a build plate. The toolhead moves in X-Y to draw each layer; the bed (or toolhead) moves in Z to start the next.
Every Bambu, Prusa, Creality, Voron, and Anycubic FDM machine works this way. The patent expired in 2009, which is why the home 3D printing market exists at all.
Why it matters
FDM is cheap, the materials are cheap, and the parts are usable straight off the printer. It is the right choice for functional parts — brackets, jigs, replacement knobs — and for any large print where SLA would cost too much in resin.
The trade-off is layer lines and limited resolution. Fine surface detail and tiny features come out better on resin printers. FDM parts are also anisotropic — weaker along the layer direction than across it.
Common confusion
FDM and FFF (Fused Filament Fabrication) are the same process. FDM is Stratasys's trademark; FFF is the open-source name coined by the RepRap project to avoid the trademark. Manufacturers alternate between the two depending on legal posture.