The vast majority of parliamentarians do not hold ministerial or shadow ministerial office and are known as backbenchers.
They are so-called because they sit on the back benches of the Commons or Lords - ministers and their opposition counterparts sit on the front benches.
Backbenchers are also sometimes known as private members and thus a backbencher can introduce an original idea for legislation in the form of a Private Member's Bill.
Backbenchers have more freedom to speak as they are not as constrained by loyalty to the government.
This can also pose problems for the party whips who try to impose party discipline.