A caster level check is successful if a roll of 1d20+your caster level is at least the DC of the check.
Caster level checks are required for instance when trying to overcome spell resistance, or to dispel magic.
This stub is related to Dungeons and Dragons Online and needs to be filled out. If you are considering filling it out, some good places to check would be both the google and ddo.com forum search pages. You can help expand it by clicking Edit at the top of the page.