What is "build a better mousetrap"

vb. (context idiomatic English) To invent the next great thing; to have a better ide

Build a Better Mousetrap is the twenty-first episode of the third series of the 1960s cult British spy-fi television series The Avengers, starring Patrick Macnee and Honor Blackman. It originally aired on ABC on 15 February 1964. The episode was directed by Peter Hammond and written by Brian Clemens.