http://en.wikipedia.org/wiki/ASCII_Drawing_Interchange_file_format Basically it's a conversion of a dimensioned 3D drawing to a language the cutting machine can use. A number of different CNC software programs use that format.

I know this because I worked on a computer for a place that does that sort of production, not because I've EVER operated a modern CNC cutting tool (but I did tell them what was wrong with one of them [:-]).