When I
planted my garden this year, I did it without a plan, and without a thought as to the kind of seeds I bought. Being late in the season, I was just happy to have a garden after three years of being gardenless (well, almost gardenless. I did try my hand at
balcony gardening last summer). Only after I got this year's garden in the ground, did I discover that most of the seeds I had planted were open pollinated kinds.
What are
open pollinated plants? The seeds from these plants will produce plants "true to type," i.e. they will produce plants just like their parents. This is obviously what a seed saver wants!
Hybrid seeds, on the other hand, are bred from specifically chosen parents to produce specifically selected traits: disease resistance, higher yield, better shipping qualities or marketing characteristics, etc. The seeds from hybrid plants are often sterile, and so produce nothing at all. Or, they may produce a "throwback" to one or the other parent, which may not have the qualities a home gardener is looking for. For the frugal gardener, using hybrid seeds means having to buy seed every year.
GMO (genetically modified organism) seed, on the other hand, is a different animal entirely. While some proponents like to say that all hybrid seeds are genetically modified, that is an extremely misleading statement. GMO seeds are developed with the
recombinant DNA technique. This technique involves creating artificial DNA sequences by combining naturally occurring DNA strands in unnatural ways. Some of the traits being developed with such technology include plants with "built in" pesticides, purportedly higher yields (something which sadly hasn't been the case, story on that
here), and plants that are specifically engineered to respond to specific pesticides (eg. "Round-Up Ready"). Since the patent on these seeds is jealously guarded, saving them is illegal. To further prevent saving these seeds, a
terminator gene has been developed for GMO field crop seed.
[An interesting sidenote: even though humans may not be able to taste the difference in GMO produce, some animals evidently can.
Click here for that story.]
Another seed term one hears used is "
heirloom". I tend to use this interchangeably with "open pollinated," but technically this is not correct. In general, heirlooms are the old open pollinated varieties, those which were planted by our ancestors. In 1951, the first hybrids were introduced, so even open pollinated varieties developed after that are not considered to be heirloom.
For the seed saver, one thing to keep in mind is that open pollinated plants
can cross with another variety, so the "true to type" part may or may not always be true. Corn and squashes are an example of open pollinated plants that can produce crosses. This presents challenges when it comes to saving seeds, but nothing that can't be overcome with good planning.

Obviously, for a either a frugal or self-sustaining gardener, open pollinated seeds are the only way to go. Garden seed is becoming increasingly more expensive to buy (along with everything else), so the prospect of being able to save all of one's own seeds is a real blessing.
If you're interested, here are a few articles on hybrid, GMO, heirloom, & open pollinated seeds and plants:
Hybrid or Open Pollinated - National Gardening Association
What is an Heirloom Vegetable? - Heirloom Vegetable. Gardener's Assistant
Grow open pollinated seeds for self-reliant gardening - Backwoods Home Magazine
Genetic Engineering and Biotechnology - Organic Consumers Association
What to Grow: 10 Easy Heirlooms - Heirloom Vegetable Gardener's Assistant
My goal is to save all my own seed. I've made a small start this year, but plan to make a concerted effort to save most, if not all, next year.