A hybrid is simply breeding two different varieties (a cross). For animals this would be like breeding a Holstien cow (black and white) with a Jersey bull (brown) you will get a calf that is mixed (perfectly healthy natural process). GMO crops are Geneticly manipulated at the molecular level. This involes using a virus to force foreign DNA into genes. This would be like breeding a cow to have a calf with 6 legs or 2 heads or a cow that produces chocolate milk. (they have actually genenticly modified a goat to milk silk!)
I understand that Alex Jones makes out Hybrids to be bad (not a big fan)
The main disadvantage of a Hybrid over a Heirloom is that you cannot save your seed from a hybrid and get predictable results. But in no way is this the same as GMO.
http://www.responsibletechnology.org to learn more on this
Download free mp3's of Dr. Wallach's radio show "Dead Doctors don't Lie" here: