The Opposition are the political parties in the House of Commons other than the largest or Government party. They are called the Opposition because they sit on the benches opposite the Government in the House of Commons Chamber. The largest of the Opposition parties is known as Her Majesty's Opposition. The role of the Official Opposition is to question and scrutinise the work of Government. The Opposition often votes against the Government. In a sense the Official Opposition is the "Government in waiting".
contributed by user local yokel