Support material is temporary structure added during 3D printing to hold up overhangs, bridges, and other shapes that would otherwise sag or collapse while being built layer by layer. It is usually designed to be removed after printing, either by snapping it off, dissolving it, or trimming it away.
It matters because supports can make the difference between a failed print and a usable part, especially for complex geometry. In practice, slicer software decides where supports are needed based on the model’s shape and the printer’s limits. The tradeoff is that supports add time, use extra material, and can leave rough surfaces where they touch the part. For that reason, support-reduction methods try to change the geometry so less temporary structure is needed.