A solid cylinder or disk that fits snugly into a larger cylinder and moves under fluid pressure, as in a reciprocating engine, or displaces or compresses fluids, as in pumps and compressors.

• 活塞一种可装到更大的筒里且在液压下移动的固体小筒或碟子，如在往复式发动机中，也可用于更换或压缩液体，如在水泵和压缩机上