A protocol is a standard that defines procedures and rules for communication. For example, the following Internet technologies, among others, are standardized in RFCs (Request for Comments) issued by the IETF (Internet Engineering Task Force).
IP: Internet Protocol, RFC 791
TCP: Transmission Control Protocol, RFC 793
UDP: User Datagram Protocol, RFC768
HTTP: Hyper Text Transfer Protocol, RFC7231
https://www.ietf.org/.