An agreed-upon format for transmitting data between two devices. The protocol determines the following: the type of error checking to be used , the data compression method (if any), how the sending device will indicate that it has finished sending a message,and how the receiving device will indicate that it has received a message.
Meaning of PROTOCOL in English
DAX English glossary of key connectivity terms. Английский глоссарий основных терминов по коммуникациям DAX. 2012