(law) The lawyers and staff who argue on behalf of another in court.
(politics) The ability to elect a representative to speak on one's behalf in government; the role of this representative in government.
(mathematics) An object that describes an abstract group in terms of linear transformations of vector spaces; (more formally) a homomorphism from a group on a vector space to the general linear group (group of all bijectivelinear transformations) on the space.