Definition: A protocol is simply a set format for exchanging information. When you dial a telephone number, the number must be in a set format to be understood. In one group of countries (the US and Canada), that format is "(123) 456-7890", but in others it is "01234 567890" (the UK) or "01 23 45 678" (Switzerland). Like dialling a telephone number, a program must relay information in a certain format to be understood by other programs on other computers. These formats are called protocols.