The C shell, commonly referred to as csh, is a Unix shell that provides an interface for users to interact with the operating system. It was developed by Bill Joy in the late 1970s and is known for its C-like syntax, making it easier for programmers familiar with the C programming language to use. Csh includes features such as command history, job control, and scripting capabilities, allowing users to automate tasks. It also supports aliases and built-in arithmetic operations, enhancing user productivity. Despite its popularity, it has been largely supplanted by more modern shells like bash and zsh.