H.264/Advanced Video Coding (AVC) is an industry standard for video compression. The H.264 standard is also known as MPEG-4 Part 10 and is a successor to earlier standards such as MPEG-2 and MPEG-4. An ITU standard for compressing video based on MPEG-4 that is popular, especially for high-definition video. AVC stands for Advanced Video Coding. Actually its identical to H.264 so you can find it as H.264, H.264/AVC, H.264/MPEG-4 AVC or MPEG-4 Part 10 (it can be twice as efficient as MPEG-4 Part 2).
Taking advantage of today's high-speed chips, H.264 delivers MPEG-4 quality with a Frame size up to four times greater. It can also provide MPEG-2 quality at a reduced data rate, requiring as Little as one third the original bandwidths. You can think it as the "successor" of the existing formats (MPEG-2, DivX, XviD etc) as it aims in offering Similar video quality in half the size of the formats mentioned before (this reduction enables burning one HD Movie onto a conventional DVD).