Gerber format
The Gerber format is an open ASCII vector format for 2D binary images. It is the de facto standard used by printed circuit board (PCB) industry software to describe the printed circuit board images: copper layers, solder mask, legend, etc.
The standard file extension is .GBR or .gbr though other extensions are also used.
There are two major generations of Gerber format:
Extended Gerber, or RS-274X. This is the current Gerber format.
Standard Gerber, or RS-274-D. This obsolete format is deprecated. It is superseded by Extended Gerber.
Usage
Gerber is the standard input format for photoplotters in PCB fabrication and all other fabrication equipment that needs digital images, such as legend printers, direct imagers or automated optical inspection (AOI) machines or for viewing reference data in different departments.
Gerber files also contains a 'stencil' layer for solder paste and the central locations of components to allow the PCB assembler to create the stencil and place and bond the components.