MPEG-4 AVC and H.264
MPEG-4 AVC is MPEG-4 part 10, ISO/IEC 14496-10, and is technically identical to ITU H.264 standand. so H.264/MPEG-4 AVC is commonly expressed.
H.264/MPEG-4 AVC wikipedia
H.264 was developed by the ITU-T Video Coding Experts Group (VCEG) together with the ISO/IEC JTC1 Moving Picture Experts Group (MPEG). The project partnership effort is known as the Joint Video Team (JVT). The ITU-T H.264 standard and the ISO/IEC MPEG-4 AVC standard (formally, ISO/IEC 14496-10 – MPEG-4 Part 10, Advanced Video Coding) are jointly maintained so that they have identical technical content. The final drafting work on the first version of the standard was completed in May 2003, and various extensions of its capabilities have been added in subsequent editions. High Efficiency Video Coding (HEVC), a.k.a. H.265 and MPEG-H Part 2 is a successor to H.264/MPEG-4 AVC developed by the same organizations, while earlier standards are still in common use.
MPEG-4 part 2, ISO/IEC 14496-2, is a encoding standand for video and is different with MPEG-4 AVC/H.264.