zlib is a software library used for data compression. It allows developers to reduce the size of files and data streams, making storage and transmission more efficient. The library is widely used in various applications, including web browsers and file formats like PNG and ZIP. The main feature of zlib is its ability to compress data using the DEFLATE algorithm, which combines the LZ77 algorithm and Huffman coding. This makes it effective for compressing text and binary data. zlib is open-source and available for multiple programming languages, making it accessible for developers worldwide.