Is an end system that is on the sending side of the communication between Hosts.
In reality, Hosts take turns being the Client and the server during a connection, since they send to and receive from each other. But the distinction is nonetheless used since one side, called the client, tends to receive more data while the other, called the server, tends to send more data.
Servers also tend to have more powerful hardware, that stores and distributes web pages, stream video, relay e-mail, etc.