The Internet Protocol Suite (usually referred to as just TCP/IP)1 consists of a number of different protocols at different levels or “layers.” For our purposes, three protocols provide the fundamental communications mechanisms. All other defined protocols are referred to as user-level protocols (e.g., HTTP, used later in this web page).
[1] It should be noted that although the Internet seems to have conquered the world, there are other networking protocol suites in existence and in use.