According to the “Ask Dr. Knowledge” column in the Boston Globe (10/31/00):

Hybridization is a word used to describe any time when genetic material from one organism is mixed with genetic material that has different heritable characteristics. There are many ways to do this.

For example, you can just “cross” two species – if they are similar enough they can mate and the offspring will have some genetic characteristics of each of the parents. It will be a “hybrid,” something that’s seen quite often in the plant world with flowers and different kinds of food-producing plants. Most corn we eat today, for example, is a hybrid, as are most tomatoes and other vegetables.

When things can’t mate, you can still mix genetic information from two different species, but you have to do it in the laboratory with special techniques.

Genetic altering is often accomplished by hybridization – and sometimes naturally – but literally the term indicates that you’ve modified the genes of something.