A compression standard derived from LZ77; it is reportedly used in zip, gzip, PKZIP, and png, among others.
Unlike LZW, deflate compression does not use patented compression algorithms.
Used as a verb to mean to compress (not decompress!) a file which has been compressed using deflate compression. The opposite, inflate, means to decompress data which has been deflated.
Deflate is described in RFC 1951.