The definition usually used in biochemistry: "peptides with fewer than about 10-20 resides" are also called oligopeptides. For those with more than 10-20 residues, they are called polypeptides. [1]
References:
1. International Union of Biochemistry. Nomenclatures and symbolism for Amino Acids and Peptides. Pure Appl. Chem. 1984, 56:595-624 (LINK)