I've had to suffer through Prolog in a languages class, as well as in a prolog lab class I elected to take over Java.... 🙂
As daMachine mentioned, it's a logical language. Everything is based on rules and evaluations of those rules. You can apparently accomplish just about anything, but you have to be a little tricky about how you go about solving the problems. My Prof always boasted he could write a simple pascal compiler in 100 lines... but then again, he's been working with Prolog for many years and has written a few books about it. His field was mostly natural language processing, so I have a feeling Prolog is probably fairly useful for that as well.
Personally, I can't come up with any real-world practical uses for Prolog. It COULD be used as a database system, or for AI (same prof uses Prolog to teach an honours AI course as well). More experience with Prolog would most likely yield quite a few uses.
If you're just up for some punishment, and many hours of smashing your head against your keyboard, give it a try. It definately makes you think and solve problems in a completely different way.