CCK (27-33) is the C-terminal heptapeptide of cholecystokinin (CCK)[1].
References
[1] Schiller PW, et al. Unsulfated C-terminal 7-peptide of cholecystokinin: a new ligand of the opiate receptor. Biochem Biophys Res Commun. 1978 Dec 29;85(4):1332-8. DOI:10.1016/0006-291x(78)91149-x