The Gerber file format is the de facto standard for printed circuit board (PCB) design data transfer, called the backbone of the electronics fabrication industry. All PCB design systems output Gerber files and all PCB fabrication software can handle them, enabling PCB professionals to exchange PCB design data securely and efficiently.
Gerber layer files represent copper layers, solder mask, legend, and drill and route data. Attributes provide meta-information about these images, such as whether a graphics object is an SMD pad, a via pad or a fiducial, or net names of connections. The Gerber job file transfers PCB fabrication characteristics, such as thickness or finish, in a standardized and machine readable manner. The Gerber format is simple, compact and unequivocal. Thanks to its use of printable 7-bit ASCII characters, it is portable, human-readable and easy to debug. Implementations are thoroughly field-tested and debugged.
A tutorial: the chapter “Overview of the Gerber Format” in the specification
Examples of PCB fabrication data sets
Test files, to help debug implementations
"Gerber is the only data format, as far as I know, that has *dropped* enough historical burdens to remain lively, based on current practice deliberately surveyed. The result is, of course, a specification easy to read and to implement correctly." - Frog Chen