Protocol HTTP for example defines the format for communication between internet browsers and web sites. Think of it as the language spoken between computers to help them communicate more efficiently.
A protocol is a set of formalized rules that explains how data is communicated over a network. TCP Port 53 may use a defined protocol to communicate depending on the application. Looking for information on Protocol TCP 53? This page will attempt to provide you with as much port information as possible on TCP Port 53.