1. 1. The act or process of compressing.
   2. The state of being compressed.
2. 1. The process by which the working substance in a heat engine, such as the vapor mixture in the cylinder of an internal-combustion engine, is compressed.
   2. The engine cycle during which this process occurs.
3. Computer Science. The process by which data is compressed into a form that minimizes the space required to store or transmit it.

The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2009. Published by Houghton Mifflin Company. All rights reserved.