Adobe Illustrator Artwork
Adobe Illustrator Artwork (AI) is a proprietary vector graphics format used by the Adobe Illustrator program.
The original format of these files was known as "PGF", but it was later embedded in a PDF wrapper for compatibility with that format. The format is also related to Encapsulated PostScript (EPS), and some versions of the file format are made to be compatible with that. Some forms of the file have multiple versions of the data embedded in it for multi-format compatibility.