Definition - What does Thick Client mean?
A thick client is one of the components in client-server computing architecture that is connected to the server through a network connection and doesn’t consume any of the server's computing resources to execute applications.
A thick client may also be known as a heavy, fat or rich client.
Techopedia explains Thick Client
Thick clients are generally implemented in computing environments when the primary server has low network speeds, limited computing and storage capacity to facilitate client machines, and/or there is a need to work offline.