The iron peak is a local maximum in the vicinity of Fe (V, Cr, Mn, Fe, Co and Ni) on the graph of the abundances of chemical elements, as seen below.

For elements lighter than iron on the periodic table, nuclear fusion releases energy. For iron, and for all of the heavier elements, nuclear fusion consumes energy, but nuclear fission releases it. Chemical elements up to the iron peak are produced in ordinary stellar nucleosynthesis. Heavier elements are produced only during supernova nucleosynthesis. This is why we have more iron peak elements than in its neighbourhood.