Which of the following best describes the function of a 'tag' in a PLC?

A 'tag' in a Programmable Logic Controller (PLC) system refers to a symbolic name assigned to a specific data location within the controller's memory. This makes option B the best description of its function. Tags are used to represent various data types, including inputs, outputs, and internal variables, allowing programmers to reference these memory addresses more intuitively during programming and configuration.

By using tags, programmers can easily understand what each memory location represents without needing to recall the actual memory address, which may be complex and not easily remembered. This enhances code readability and maintainability, making it simpler for others to understand and modify the program later.

The other options do not accurately capture the primary purpose of tags within a PLC system. For instance, tags are not synonymous with input devices, nor do they solely represent user interface elements or identify safety parameters. Instead, they serve as a bridge between user-friendly naming and specific memory locations, streamlining the programming process and enhancing the clarity of the control logic.