A client.
The computer on a network that requests resources from the server is called the client. The server may also be used to implement administrative security for the client computers.
Server
A
The applications installed help the networked server manage requests from multiple clients for different services. The server receives the requests and delegates them.
A Web Server.
concurrent server is a server which can handle multiple requests at a time.
Server's function is to respond for the client's application requests
A server is a computer system or software that provides functionality or resources to other computers, known as clients, over a network. Servers typically perform tasks such as storing and managing data, processing requests from clients, and providing access to shared resources like files or applications. Servers run continuously and are designed to handle multiple client requests simultaneously.
There are no friend requests in Minecraft unless the server you are on has a specific mod for it. If so, ask around the server for specific instructions.
An application or browser
Client.
A server waits for a request by a client. When the client sends the requests, the server answers to it. Examples are file servers, that listen to requests from clients wanting to save or retrieve files; print servers that wait for requests to print (and then print them); DHCP servers that wait for requests to provide IP addresses; etc.