Protocol are communication rules between computers. TCP/IP protocol is used for communication between computers. It is just like language which is understandable at both ends. If a person knows English and the other Italian than they can't communicate effectively. Just like this for communication between computer there are certain protocols for certain applications.
Protocols are procedures/rules used by networked computers to communicate. For communication to take place, the two computers must have a protocol in common. There are many different protocols now and they each have there advantages and disadvantages. A protocol is used so that computers can communicate and send data from one computer to another.
TCP/IP: A protocol developed for the internet to get data from one network device to another, it use to communicate
Probably the popularity of the internet tcp/ip is the communications language of the internet.