GMO stands for Genetically Modified Organism. Other names for the process include Genetic Engineering (GE) or Genetic Modification (GM), which are one and the same.
How is a GMO Different from Hybridization / Cross-Breeding?
Genetic modification is the process of forcing genes from one species into another entirely unrelated species. Unlike cross breeding or hybridization—both of which involve two related species and have been done without ill effects for centuries—genetic engineering forcefully breaches the naturally-occuring barriers between species.
Example: Corn + DNA from soil bacteria that is naturally immune to RoundUp herbicide + e.coli bacteria + soil bacteria that causes tumors in plants (which enables the plant’s cell wall to be breached) = RoundUp Ready Corn (one of several RoundUp Ready crops engineered by Monsanto).