There is no difference. A cock is a mature male chicken, also called a rooster. A cockerel is a immature male chicken.

ha that IS a difference lol. and the question was between a rooster and a cockerel, not a cock

Well, etymologically, the difference is in the USE of said bird. 'Rooster' is an adult male bird kept for EATING, or one who occupies the roost, as opposed to a bird kept for breeding purposes....
Hence I have a cage of roosters without any hens, that I will slaughter for the table, but I have only one cock with each group of hens. A bird over a year, but still edible is a rooster, a bird over 5 and not headed for the table, but kept for breeding is a cock.

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