Deflate is a lossless data compression algorithm that uses a combination of the LZ77 algorithm and Huffman coding. It was originally defined by Phil Katz for version 2 of his PKZIP archiving tool and was later specified in RFC 1951.
The original algorithm as designed by Katz was patented as US patent 5051745 and assigned to PKWARE. Deflate is widely thought to be implementable in a manner not covered by patents. This has led to its widespread use, for example in gzip compressed files, PNG image files and the ZIP file format for which Katz originally designed it.
Read more about DEFLATE: Stream Format, Encoder/compressor, Using Deflate in New Software, Decoder/decompressor