A protocol is a plan to coordinate one or more activities within a specific social context.
Protocol often especially means a standardized procedure for performing a sequential signaling process, such a repeated exchange of signals of predictable types.
Protocols are common in ungoverned relationships between autonomous or sovereign agents. They're also common in governed contexts, as part (or all) of policies. They're often perceived as recipes, guidelines or rules in specific social contexts, such as collectives and communities. (Each protocol can, complexly, contain any combination of guidelines and rules.)
Protocols facilitate effective and efficient communications in diverse social contexts. Some are used for live communication or telecommunication, including digital networking protocols such as http.
A digital protocol may consist entirely of a standardized format for a type of signal in a specific context. However, protocols often standardize sequential processes and programs which exchange specific types of signals.