While looking through seed catalogues, you will be confronted with a plethora of terms. You should probably understand what they all mean, and what will work best for you and your garden. I am no expert, and there is a wealth of knowledge out there. Do some searches, find what other gardeners have said about different varieties you are interested in, and if you can’t decide, stick it in the ground and see if it grows.
Heirloom – Simply put, this means, that the seeds will produce a plant exactly like itself, and it’s parents, and its grandparents. They are open-pollinated (more about that below). Typically, heirlooms need to be older than 50 years, although, some places say 100 years. Whatever the magic number, they typically need to come from before we really started messing with the earth to get it to produce more and more from less and less space. (Pre-WW2). These are the same type of varieties that your great grandparents probably grew.
Heritage – This term means different things in different places. Some say that it is just an Heirloom, while others say that it needs to have “cultural or ethnic importance.”
Hybrid – Simply put, this is a cross between two plants that can cross pollinate. Although, typically, it is done by humans breeding plants based on the characteristics they possess. Think tomatoes and corn – they are the most often “hybridized.” If you look at a few seed packets, they are almost always bred to possess certain characteristics. However, hybrid does NOT mean that is has been genetically modified, and hybrid seeds and plants can be certified organic. But if you are growing a hybrid variety in the hopes of saving the seeds from it, and expecting to get the same plant in the next planting, you will likely be disappointed – the seeds saved from hybrid varieties will likely resemble one of the original parents, or be sterile. There are a few cases where hybrid varieties stabilized and can produce true to type, OP plants.
Open-Pollinated – Often stated as “OP” this means that the seeds produced will produce a plant exactly like the parent plant. This is why heirloom plants are open pollinated. As long as OP plants that can cross with others are kept separate (for example, Beets and Swiss Chard) they will produce seeds that are “true to type”. If not kept separate, then they may cross, and if the seeds are viable (and not sterile), then you end up with a hybrid.
For a little more in-depth information, check out this article.