This is not an insulting term. It simply means that the computer terminal attached to a network is capable of running applications on its own.
For example, most PC's are 'fat clients' because they can run applications without being connected to a network.
The opposite of Fat Client is 'Thin Client'
See also Thin Client in the glossary.
Challenge see if you can find out one extra fact on this topic that we haven't already told you
Click on this link: Fat Client