Outbreeding depression, as opposed to inbreeding depression, occurs when the cross breeding of different populations, as opposed to within the same population, results in a reduced level of fitness in the offspring. Conversely, inbreeding depression results when breeding within a population results in a reduced level of fitness in the offspring.
Hutchings, J.A. & Fraser, D.J. (2008). The nature of fisheries- and farming-induced evolution. Molecular Ecology, 17(1), 294-313.