zlib is a common software library used for data compression. zlib compressed data is typically written with a gzip or a zlib wrapper. zlib is something of a de facto standard, to the point that zlib and DEFLATE are often used interchangeably in standards documents, with thousands of applications relying on it for compression, either directly or indirectly.

zlib1.dll is loaded as dynamic link library that runs in the context of a process. This is typically installed with the program SnapPea published by Wandou Labs. The file is digitally signed by Wandou Technology Ltd which was issued by the VeriSign certificate authority (CA). This particular version is usually found on Microsoft Windows XP (5.1.2600.196608).