MPEG-1 is a video and audio compressed stream standard which is part of the MPEG group of standards. It can be used in a variety of containers, resulting in various file types including the popular MP3 audio format (which is based on Layer 3 of MPEG-1, and also Layer 3 of MPEG-2).
The later MPEG-2 standard is an extension of MPEG-1.
The ISO/IEC-11172 group of standards, published between 1993 and 1998, give the details of the specifications.
This standard is old enough that any patents that may have encumbered it in the past are now expired. US patents 4,472,747 and 5,214,678 are such possibly-related but expired patents. Since MP3 audio uses things from MPEG-2, there are still some unexpired patents relevant to that.