1. reduction in size: the reduction of the volume or mass of something by applying pressure, or the state of having been treated in this way
2. phase in engine: the phase in the working of an internal-combustion engine in which a combination of fuel and air is compressed in a cylinder before being ignited
3. comput reduction of computer data: a technique for reducing the number of bits required to represent text, data, or images so as to save storage space or reduce transmission time
[14th century. Via French< Latin compression-< compress-, past participle of comprimere (see compress)]
