Krav Maga is self defense. It incorporates strikes from Muay Thai, boxing and the ever popular groin kicks. Also, it teaches wrestling defense and jiu jitsu chokes.
However, the first thing taught in KM is that you should never stay on the ground in a street fight. Sounds harder than it is, but a good Krav Maga instructor shows you ways to always stay on your feet, and defend yourself just enough so you can run away.
Yes, run away.
That is the most basic principle of Krav Maga...staying alive. This isn't a sport combat where you showcase your skills and spar and prove you're the #1 KM fighter in the world. This art was invented for the streets where staying alive is doing whatever is necessary and then running away to safety.
Kicks to the groin and elbows to the back of someone's head is heavily encourage, most people think this hybrid martial art is a joke, but quite simply it's not.
The most difficult aspect of Krav Maga is finding a legit school and teacher. Once you do, however, you'll be pleasantly surprised ( like I was ).