A member of the lobby; a person who solicits members of a legislature for the purpose of influencing legislation.
Someone representing a particular special interest group at the Capitol is a lobbyist. Those at the Statehouse regularly arguing their case, whether purely out of conviction or doing it for pay, must register with the chief clerk of the House and the secretary of the Senate. The number of registered lobbyists often exceeds 500 per session.
Individuals who represent the causes of a group, organization, association, or industry (or just themselves) and express those views to Members of Congress and congressional committees considering legislation in their areas of interest. Lobbyists must formally register with the Clerk of the House and Secretary of the Senate and reveal their expenditures. The term comes from the first years of Congress, when many Members lived in hotels during congressional sessions. People seeking to influence legislation would hang out in the lobby of the hotels seeking to speak to the Members as the came and went.