Zlib is a software library used for data compression. It provides a way to reduce the size of files, making them easier to store and transmit. The library is widely used in various applications, including web browsers and file formats like PNG and ZIP. Developed by Jean-loup Gailly and Mark Adler, Zlib is known for its efficiency and speed. It uses the DEFLATE compression algorithm, which combines the LZ77 algorithm and Huffman coding. Zlib is open-source, meaning anyone can use or modify it, contributing to its popularity in software development.