A computer that includes an operating system and installed applications and can run either as a standalone or in a server environment. See also thin client.
In client/server computing, a client is said to be "fat" (or "thick") when it handles a high amount of the application logic and data management tasks, rather than having these tasks executed remotely on the server. See client/server and thin client.
Your average desktop PC that does most of the application processing and stores software and data on its hard disk and is network ready.