The term 'RULES: ABBR.' can be solved by the two four-letter words REGS and STDS. REGS is an abbreviation for regulations, which are a set of rules or guidelines established by an authority, organization, or community to regulate behavior. STDS is an abbreviation for standards, which are a level of quality or attainment that is considered acceptable or desirable. Both regulations and standards are used to establish rules and guidelines in various contexts.