A member of parliament (MP) is the representative in parliament of the people who live in their electoral district. In many countries with bicameral parliaments, this term refers only to members of the lower house since upper house members often have a different title. The terms congressman/congresswoman or deputy are equivalent terms used in other jurisdictions. The term parliamentarian is also sometimes used for members of parliament, but this may also be used to refer to unelected government officials with specific roles in a parliament and other expert advisers on parliamentary procedure such as the Senate parliamentarian in the United States. The term is also used to the characteristic of performing the duties of a member of a legislature, for example: "The two party leaders often disagreed on issues, but both were excellent parliamentarians and cooperated to get many good things done."

A caucus is a meeting or grouping of supporters or members of a specific political party or movement. The exact definition varies between different countries and political cultures.