The cheap seats in a theater. Also used to refer to the rowdiest persons in an audience.

This saying comes from late 19th century vaudeville, where the worst seats were the balcony. The audience would not only heckle bad performers but throw peanuts as well, which at the time was the common theater snack.

Name of the live studio audience for The Howdy Doody Show, an American television program which ran on NBC from 1947 to 1960.

Their critical role came at the top of the show, when Buffalo Bob would ask: "Hey, kids, what time is it?"
And the Peanut Gallery would shout: "It's Howdy Doody time!" at which point the theme music would begin, and soon Buffalo Bob along with every kid in the studio audience would sing (usually as loud as they possibly could) the theme song.