What is the difference between BCS championship and National Championship?

Answer 1

This is acctually a complicated question, I hope this helps.

The NCAA does not grant an official national championship in the FBS (formerly Division 1-A), instead the highest level of an official national championship is in the FCS (formerly Division 1-AA). As for the FBS, the national championship has traditionally been decided by two to three sets of polls voted on by members of the media or coaches. The BCS was formed to try and put the two top teams together in a "national championship" game using the polls to determine those teams. Since the AP poll pulled out of the BCS, however, the champion is decided by the winner of the BCS title game AND the Associated Press. So there could theoretically be a BCS champion and an AP champion, both of which would be regarded as the "national champion" for that year. However, 2003 was the last time this happened (LSU won the BCS, but the AP selected USC.)

There are also a handfull of mathematical systems that grant a "national championship" but they are not typically recognized by schools, fans, or the media.