Protocol is a set of rules. Now consider that you are driving a car. You have to follow some set of rules for that. Why was that rules put? It was posed on all drivers so that the transportation is smooth and safe. Similarly in networking the protocols were set up so that the transportation of your message over the network is smooth and safe.
A standard way of communicating across a network. A protocol is the "language" of the network. A method by which two dissimilar systems can communicate. TCP is a protocol which runs over a network.
protocol (from the Greek protocollon, which was a leaf of paper glued to a manuscript volume, describing its contents) is the special set of rules that end points in a telecommunication connection use when they communicate. Protocols exist at several levels in a telecommunication connection. For example, there are protocols for the data interchange at the hardware device level and protocols for data interchange at the application program level. In the standard model known as Open Systems Interconnection (OSI), there are one or more protocols at each layer in the telecommunication exchange that both ends of the exchange must recognize and observe. Protocols are often described in an industry or international standard.
firstly I would like to say protocol is a set of rules which is could be any thing and if I talking about the wht is the role of protocol in networking so it is the rule of how to communicate wid one device to other device. and protocol is defined how to communicate one device to another device.