A pipe wrench is a special adjustable wrench used to turn pipes. Usually lead pipes. The pipe wrench is designed with a specially floppy moving part and gripping surfaces that are serrated and sharp. These two things allow the pipe wrench to really bite into a pipe.

Pipe wrenches are usually big, and painted red. Don't know why - it's tradition.

May also be known as a plumber's wrench, because plumbers carry them.

I once saw a selection of pipe wrenches at a Home Depot. the sizes went from a fairly small 10" long one to a preposterous 3' long behemoth. I think they use it to turn the Hoover Dam on and off. Interestingly, the design just scaled up - just different sizes, with no change in design as they got bigger.

Don't use a pipe wrench on anything else but a pipe - you'll end up stripping the nut you are trying to loosen, and end up making gouges on everything. You should use either a closed-end wrench or a crescent wrench for those jobs (don't even get me started on adjustable wrenches). The only good thing to do with a pipe wrench besides wrenching pipes is clocking Colonel Mustard over the head in the library.