G1 is one of the most essential G‑code commands in FDM 3D printing. It performs a linear movement, either:

with extrusion (if an E value is included)
or without extrusion (if no E value is present)
G1 controls almost all printed paths: perimeters, infill, supports, top layers, etc.

Codesample

G1 X120 Y80 E0.45 F1800