The mod_deflate module provides the DEFLATE output filter that allows output from your server to be compressed before being sent to the client over the network. The gzip encoding is the only one supported to ensure complete compatibility with old browser
mod_deflate is an optional module for the Apache HTTP Server, Apache v2.0 and later. It is based on Deflate lossless data compression algorithm that uses a combination of the LZ77 algorithm and Huffman coding.