A server is defined as a computer or computer program which manages access to a centralised resource or service in a network. Put simply, a server is an instance of a computer program that responds to requests made by another program known as a client.
The word ‘server’ dates back to the mid 20th century and originates from queuing theory, which is the mathematical study of waiting lines of queues. The use of the word server in computing was first seen in documents describing ARPANET, the predecessor of the Internet, in 1969.
Servers work as part of the client-server model, a model which denotes the serving of data for clients. This reflects the purpose of a server which is to share data, distribute work and share resources. Almost the entire Internet is based on the client-server model, with millions of servers connected to the Internet running continuously across the world. The client-server model sits in contrast to peer-to-peer where the relationship is on-demand reciprocation.