n. A proprietary UNIX utility for reducing the size of data files. Files compressed with this utility have the extension .Z added to their names.vb. To reduce the size of a set of data, such as a file or a communications message, so that it can be stored in less space or transmitted with less bandwidth. Data can be compressed by removing repeated patterns of bits and replacing them with some form of summary that takes up less space; restoring the repeated patterns decompresses the data. Lossless compression methods must be used for text, code, and numeric data files; lossy compression may be used for video and sound files. See also lossless compression, lossy compression.