Industry-standard file format describing each copper layer of a PCB. What fabs need.
How it looks
Real geometry: CORE3588 copper, drawn from our board file (2D plan view)
Top copper of CORE3588, drawn from the board file. This is exactly what the top-copper Gerber (core3588-F_Cu.gtl) describes: every track, pad and the ground fill, as flat shapes. Dark lines are gaps where copper will be etched away.
Real geometry: CORE3588 copper, drawn from our board file (2D plan view)
Inner layer 1 (core3588-In1_Cu.g1): almost solid copper, a ground sheet, with a clear ring for every hole that passes through it.
How it works
Where it fits
Gerbers are what you send the fab, together with the drill file and the job file. For assembly you also send a BOM and a CPL.
Each Gerber is one layer; the fab's CAM team reads them and may answer with an EQ.