Genetically modified (GM) foods have been around since the 1990s, and these days GMOs (GM organisms) constitute the majority of US acreage for plants like soybeans and corn. Unlike new varieties of crops and livestock created through the process of crossbreeding as in the old days, GMOs have their DNA manipulated in the lab, with new genes inserted, deleted, turned on/off, and the like. (Genes can even be inserted from one species into another unrelated one.)
Pro-GMO types — especially ag business giants like Monsanto and their friends — argue that GMOs are safe, cost-effective, and productive. Critics argue that the health and environmental consequences can’t possibly be known given the limited, narrowly focused research that’s been conducted. For example, long-term studies to try to understand the consequences of Round-Up resistant GM alfalfa mixing with non-GM alfalfa outside the lab in the real world haven’t been done.
Candidate Obama said consumers had a right to know whether GMOs were in their foods or not. President Obama’s administration, though, hasn’t followed through. Meanwhile, the administration has also approved the introduction of new GMOs. For additional details, check out this article from The Daily Beast, and this piece from NPR.