Each of these words refers to the highest point of something, with top being the term in widest use (the top of the hill, the top of the house). Peak means a pointed extremity, the pointed top of a hill or mountain (peak of a roof, peak of a cap, peak of Mount Monad-nock). Summit is close in meaning to peak,"the highest point of an elevation of any kind": "The summit of the hill was covered with wild flowers." Related words which also suggest the figurative meanings of summit, peak, and top include apex, pinnacle, zenith, elevation, height, climax, and acme. Thus one refers to a student at the top of his class as one who has reached the summit of his goals. When traffic is heaviest, it is at its peak. Diplomats conduct talks at the summit.
Dictionary of problem words and expressions. Harry Shaw. 1975.