A style of rock that originated in late 60s - early 70s Germany. Musically it seems to extol the machine (Kraftwerk being a leading example) or more commonly industrial decay (Can, Faust, Neu, Einsterzende Neubauten). Amon Duul II actually employed jackhammers in one stage show, to the horror of the concert hall management. Think of punk crossed (however improbably) with prog rock, sometimes with a funky groove underneath it all. Some people regard more ambient bands like Tangerine Dream and Popul Vuh as being part of Krautrock as well.
"What's that god-awful racket?"
"It's Krautrock, mom!"