OMB is a short way of writing Office of Management and Budget. It is a United States government office that works for the President. Its main job is to help write the President's budget — the big yearly plan for how much money the country will take in and how much it will spend — and to check other offices' spending and rules. News stories often say 'the OMB said…' as if the office itself were speaking; though actually they often mean the director at the top, and a new President usually puts a new person in that chair, so the OMB is both a standing office and a political voice. You will almost never hear this about Taiwan or Britain. It is a Washington name. If you do not follow US news, you can treat it as the name of that one office and move on.