Protocols are rules that govern a conversation: who talks first, what language is used, what replies are like. They keep the conversation polite and organized.
Network protocols govern communications involving networks. They are often specified by standards organizations so that conversations can be conducted between entities previously unknown to one another.
These are types of conversation that often occur within dialogues that follow protocols. Most often they are "round-trip protocols", meaning a pattern of queries and replies (sometimes called requests and responses) related to a specific situation.