A street elbow (sometimes called a street ell or service ell) is a type of plumbing or piping fitting intended to join a piece of pipe and another fitting at an angle. The difference between a street elbow and a regular elbow is the gender of its two connections.
A regular elbow has a female connection on each end, so it can join two male pipes. Each end of the elbow could be a hub—to receive a straight pipe—or have a female pipe-thread—to receive a male threaded pipe. Instead, a street elbow has a female fitting on one end but a male fitting (either straight or threaded) on the other. The advantage of the street elbow is that it can be connected directly to another fitting without having to use an additional short connecting piece (a pipe nipple).
