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Hear, hear is an expression used as a short, repeated form of hear him/her. It represents a listener's agreement with the point being made by a speaker.
It was originally an imperative for directing attention to speakers, in the British Parliament, and has since been used, according to the Oxford English Dictionary, as "the regular form of cheering in the House of Commons", with many purposes, depending on the intonation of its user.
Its use in Parliament is linked to the fact that applause is normally (though not always) forbidden in the chambers of the House of Commons and House of Lords.
https://en.wikipedia.org/wiki/Hear,_hear