What term describes documentation that explains the purpose of a rung in a PLC program?

The term that describes documentation explaining the purpose of a rung in a PLC program is known as a rung comment. In programming, comments are essential for improving readability and understanding, particularly in complex systems such as PLCs. Rung comments provide essential context to each rung, allowing other programmers and maintenance personnel to quickly grasp what each rung is intended to accomplish without deciphering the entire program logic. This practice enhances collaboration, troubleshooting, and long-term maintenance of PLC programs, making it easier to maintain systems over time.

Other options like documentation tag or instruction guide do not specifically refer to the explanatory content provided for individual rungs. A program log typically documents changes and updates to the entire program rather than explaining individual elements within it. Thus, rung comments are the precise tool used in PLC programming for this purpose.