90-Degree Pipes are a type of pipe fitting used to connect two pipes at a 90-degree angle. They are commonly used in plumbing and other piping systems to change the direction of the flow of liquid or gas. ELLS is the abbreviation for Elbows, which are the most common type of 90-Degree Pipe. Elbows are curved pieces of pipe that allow for a change in direction of the flow of the material being transported.