Krav Maga (Hebrew קרב מגע: "contact combat") is a self-defense and military hand to hand combat system developed in Israel. It came to prominence following its adoption by various Israeli Security Forces; now more widely in use including by the special forces of other countries. The version of Krav Maga taught in civilian martial arts classes is more often a simplified version that emphasizes personal self-defense, and is likely to exclude the killing techniques taught to the military, or the holds and come-alongs taught to police forces; there are legal proscriptions in some countries which govern and constrain the teaching of hazardous or life-threatening techniques to civilians. English-speakers often shorten the term to Krav.
Etymology
The generic name in Hebrew is usually translated as "close combat." The word maga (מגע) means "contact". The word krav (קרב) means "fight" or "battle." A translation like "contact combat," though, can be misconstrued as something like "kickboxing" or "full contact karate."
As a historical note, the original name of Krav Maga was Kapap (sounds like "ka-PAPP") which was an acronym for Krav Panim el Panim, face-to-face combat.