A caveat is a warning or admonition. It can also mean a detail or condition to be taken into consideration while doing something.
After country icon Minnie Pearl died, Rod Harris commissioned a statue. The donation came with one caveat: The statue had to stay on one exact spot in downtown Centerville, Tenn. (USA Today)
Europeans have more confidence than Americans do in his [Barack Obama] ability to deal with international issues ranging from terrorism to Russia to the Middle East. Europeans trust Mr. Obama to handle such issues more than they do their own leaders. But there are three important caveats. One is Central and Eastern Europe, where the Obama magic works less well… (NY Times)