The term FIRM: ABBR. can be solved by two abbreviations, CORP (4 letters) and ESQ (3 letters). CORP stands for corporation, which is a type of business entity that is legally separate from its owners and has the capacity to own property, enter into contracts, and pay taxes. ESQ stands for esquire, which is a title of respect used in the United Kingdom and the United States for lawyers, usually of higher rank than a barrister.