Hybridization, the making of a hybrid, is the a cross fertilization of two varieties of the same species the product of which will have a higher yield than either of the parent lines, a phenomena known as hybrid vigour. There are various form of hybrid, i.e. potential increase in yield.
Not all crosses produce the hybrid vigour, and it is the skill and knowledge of the breeder that is behind all hybridization programme. It is skill and knowledge of the seed producers and seed merchants that maintain the purity of parent material and produce the final hybrid seed.