Performance of offspring that is greater than the average of the parents.  Usually referred to as the amount of superiority of the crossbred over the average of the parental breeds.  Also called hybrid vigor.

Phenomenon in which the F1 generation has higher fitness than the parental strains or subpopulations that were crossed (mated) to produce them. © 2004 by Sinauer Associates, Inc. All rights re [..]

A genetic phenomenon that describes the effects of the improved or increased function of any biological quality due to selective breeding to generate offsprings that are genetically superior to their [..]

The increase in fitness

The superiority of hybrids over either inbred parent; a.k.a. hybrid vigor.

see hybrid-vigour.

(n) (genetics) the tendency of a crossbred organism to have qualities superior to those of either parent

The adaptive superiority of the heterozygous Genotype with respect to one or more Characters in comparison with the corresponding Homozygote.

The phenomenon in which the heterozygous genotypes with respect to one or more characters are superior in comparison with the corresponding homozygous genotypes in terms of growth, survival, phenotypi [..]

Performance of offspring that is greater than the average of the parents. Usually referred to as the amount of superiority of the crossbred over the average of the parental breeds. Also called “hybrid vigor.”

(genetics) The tendency of cross-breeding to produce an animal or plant with a greater hardiness than its parents; hybrid vigour

(French : hétérosis) Advantage of heterozygote genotypes over homozygote genotypes of their parents.