Gerber format
From Just Solve the File Format Problem
The Gerber format is not a type of baby food, but a vector image format (bi-level 2D) used to describe printed circuit board designs. It exists in two formats, the Standard Gerber (RS-274-D, now deprecated) and Extended Gerber (RS-274X, in common use now).
The Gerber formats are expressed in ASCII form as sequences of commands and coordinates.
Utilities exist to convert between this and the Excellon drill format.