Which term in the Rules of Golf indicates something mandatory, with penalties for non-compliance?

The term that indicates something mandatory within the Rules of Golf is "Must." This term is used to signify requirements that a player is obligated to follow, and non-compliance leads to specific penalties outlined in the rules. The use of "Must" creates a clear and unambiguous standard that players are expected to adhere to at all times.

In contrast, terms like "May" and "Should" allow for discretionary action or suggest recommendations rather than impose strict requirements. "May" indicates an option or choice available to the player, while "Should" implies a recommended action but does not carry a penalty for not following it. The term "Deemed" often refers to a situation or action considered as such under the rules, but it doesn’t impose a mandatory action on players. Thus, "Must" is the definitive term for rules that require compliance, making it the correct choice.