A systematic pattern of deviation from norm or rationality in judgment. (Haselton et al. 2005)
Haselton, M.G., D. Nettle, and P.W. Andrews. 2005. "The evolution of cognitive bias." In D.M. Buss (Ed.). The Handbook of Evolutionary Psychology. Hoboken, NJ, US: John Wiley & Sons Inc. pp. 724–746.