Part 10: Refer to H.264.
Part 12: Refer to ISO Base Media File Format.
Part 14: Refer to MP4.
Part 15: Refer to AVC (file format).
Part 22: Refer to Open Font Format.
"MP4 audio players" don't always support the MPEG-4 file formats, sometimes supporting only the AAC audio encoding from MPEG-4, Part 3 (aka MPEG-4 Audio). These would more properly be called AAC files, with the extension ".aac".
MPEG-4 is encumbered by numerous patents, and (at least) commercial implementers have to secure licenses. Many of the licensing aspects are handled by a group called MPEG LA.