what's the difference between divx and xvid formats?

Question

and what divx and xvid means?

Answer 1

Both Divx and xvid are based on MPEG-4, part 2.

Divx is trademark of Divx corporation. Manufacturers who want to have the Divx logo - showing Divx compliance - need to pay a hefty fee to Divx.
xvid is more or less free. The main difference between the two is on some pre-processing, post-processing, and subtitle support algorithms that are not governed by MPEG-4.
I don't think there is compliance testing for xvid.