In parliamentary systems, politicians are said to cross the floor if they formally change their political affiliation to a different political party than which they were initially elected under (as is the case in Canada and the United Kingdom). In Australia though, this term simply refers to Members of Parliament (MPs) who dissent from the party line and vote against the express instructions of the party whip while retaining membership in their political party (at least for the time being).

Voting against party lines may lead to consequences such as losing a position (e.g., as minister or a portfolio critic) or being ejected from the party caucus. While these practices are legally permissible in most countries, crossing the floor can lead to controversy and media attention. Some countries like India, the Maldives and Bangladesh have laws that remove a member from parliament due to floor-crossing.