Uttam said..
A server is a computer that serves information to other computers. These computers, called clients, can connect to a server through either a local area network (LAN) or a wide area network (WAN), such as the Internet.
There are a number of different types of servers, including Web servers, mail servers, and file servers. A web server serves Web pages to computers that connect to it. It also can parse scripting languages such as PHP, ASP, and JSP. A mail server stores users' e-mail accounts and sends and receives e-mail messages. For example, when you send an e-mail to a friend, the message is sent by a mail server, using the SMTP protocol. A file server is a computer that stores files that can be accessed by other computers. File servers are often used within local networks and typically require a password or some kind of authentication to connect to it.
These are a few examples of some common servers, but several other types of servers exist. Just about any computer can be used as a server if the necessary server software is installed on it. While servers typically don't need a lot of processing power, lots of RAM and fast hard drives are helpful for dealing with heavy traffic to and from the server.