A client is an application or system that accesses a service made available by a server.
Clients are generally classified as either "fat clients", "thin clients", or "hybrid clients".
A fat client, also known as a rich client or thick client, is a client that performs the bulk of any data processing operations itself, and does not necessarily rely on the server.
A thin client is a minimal sort of client. Thin clients use the resources of the host computer.
A hybrid client is a mixture of the above two client models. Similar to a fat client, it processes locally, but relies on the server for storage data. This approach offers features from both the fat client (multimedia support, high performance) and the thin client (high manageability, flexibility).