Collagen is the protein found in animals (mainly mammals) and in humans. Native collagen is insoluble. Gelatin - generally extracted from the bones and skins of beefs, pigs or fish - is a form of collagen that we use in our foods. Because of its functional versatility, it is irreplaceable in many applications.
Collagen peptides are not exactly the same as gelatin. Both are proteins made of amino acids, but the amino chains of collagen peptides have been cut into smaller pieces through a specific hydrolysis process. Collagen peptides do not have the gelling functionality of gelatin and are soluble in cold water. They are highly digestible and bioavailable and are used in dietary supplements and functional foods because of their proven health benefits. 
Find out more about collagen peptides and their health benefits on the Peptan website.