A pipe cross is a type of pipe fitting that is used to connect four pipes of equal or varying diameters at right angles. It typically has one inlet and three outlets, or vice versa, allowing for the distribution of fluid or gas flow in multiple directions. Pipe crosses are commonly used in plumbing, HVAC systems, and industrial applications where branching of pipelines is required. They come in various materials such as stainless steel, brass, copper, and PVC, to suit different application requirements.