CHM, which stands for Compiled HTML, is a file format used to store documentation in Windows operating systems. Some synonyms for CHM include compressed HTML, Microsoft HTML help, and Windows help file. The CHM format is commonly used for software manuals, technical documentation, and user guides. Alternative file formats for storing similar types of content include PDF, HTML, and EPUB. While CHM files were popular in the past, they are now commonly replaced with online documentation or cloud-based solutions. However, many legacy software applications still rely on CHM files and continue to use them for documentation purposes.