---
title: Glossary
description: Definitions for terms used across Cloudflare Spectrum documentation.
image: https://developers.cloudflare.com/core-services-preview.png
---

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# Glossary

Review the definitions for terms used across Cloudflare's Spectrum documentation.

| Term                                               | Definition                                                                                                                                                                                        |
| -------------------------------------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| ACK (Acknowledge)                                  | The final step in the TCP three-way handshake, confirming the establishment of a connection.                                                                                                      |
| FTP (File Transfer Protocol)                       | A standard network protocol used for transferring files from one host to another over a TCP-based network.                                                                                        |
| FTPS (File Transfer Protocol Secure)               | An extension of FTP that adds support for the Transport Layer Security (TLS) or Secure Sockets Layer (SSL) cryptographic protocols.                                                               |
| layer 3                                            | The network layer in the OSI model, responsible for logical addressing, routing, and forwarding of data between devices on different networks.                                                    |
| layer 4                                            | The transport layer in the OSI model, managing end-to-end communication, error-checking, and flow control.                                                                                        |
| MQTT (Message Queuing Telemetry Transport)         | A lightweight, publish-subscribe messaging protocol often used for communication in the Internet of Things (IoT) and other resource-constrained scenarios.                                        |
| OSI model (Open Systems Interconnection model)     | A conceptual framework that standardizes the functions of a telecommunication or computing system into seven abstraction layers.                                                                  |
| proxy protocol                                     | A protocol used by network proxies to convey client connection information to the destination server, facilitating proper handling of client requests.                                            |
| reverse proxy                                      | A server that handles requests on behalf of clients, forwarding them to backend servers and managing tasks like load balancing and security.                                                      |
| SFTP (Secure File Transfer Protocol)               | A secure file transfer protocol that uses the Secure Socket Shell (SSH) protocol for encryption and authentication.                                                                               |
| SMTP Server (Simple Mail Transfer Protocol Server) | A server responsible for sending, receiving, and relaying email messages over a network, following the SMTP protocol.                                                                             |
| SYN (Synchronize)                                  | The initial step in establishing a TCP connection, where a device requests a connection with another by sending a SYN packet.                                                                     |
| SYN-ACK (Synchronize-Acknowledge)                  | The second step in the TCP three-way handshake, where the server responds to a SYN request with a SYN-ACK packet.                                                                                 |
| TCP (Transmission Control Protocol)                | A connection-oriented protocol in the transport layer of the Internet Protocol Suite, providing reliable and ordered delivery of data between devices.                                            |
| UDP (User Datagram Protocol)                       | UDP (User Datagram Protocol) is a connectionless transport layer protocol that provides fast and lightweight data transmission between devices on a network, prioritizing speed over reliability. |

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