What in Genetics is hybridization?
Hybridization in Genetics is the crossing of individuals from "pure" and dissimilar lineages in relation to a given trait, i.e., the crossing of different homozygous for the studied trait.
In Mendel's experiments with peas, for example, a plant from a green pea lineage get from self fecundation of its ascendants through several generations was crossed (cross fecundation) with another plant from a yellow lineage also obtained by self fecundation of ascendants. (The self fecundation through several generations of ascendants and the exclusive obtainment of individuals with the desired characteristics ensured that the individuals of the parental generation were "pure", i.e., homozygous for that characteristic.)