In piping systems, elbows are fittings used to change the direction of the pipeline. Commonly, there are three angles available: 45°, 90°, and 180°. Additionally, elbows with other non-standard angles, such as 60°, are included based on engineering requirements. The materials for elbows include cast iron, stainless steel, alloy steel, malleable cast iron, carbon steel, non-ferrous metals, and plastics.

Ways to connect pipes include direct welding (commonly used), flange connection, hot melt connection, electric melt connection, threaded connection, and socket welding connection, etc. They can be categorized by production process into: welded elbows, stamped elbows, expansion-formed elbows, cast elbows, and socket-welded elbows, etc. Other names: 90-degree elbows, right-angle elbows, etc.