Varieties, Lines, Hybrids, Landraces...
...What are the differences anyway?
Why the names
As a general rule, the types of varieties used in catalog descriptions derive from each species reproductive biology. In other words, some plants need to have a lot of diversity in the pollination patterns to be productive and healthy, like corn, while other plants will be able to stabilize into a variety from a single seed, pollinate itself, like beans. Simply put, that's why corn is often sold as F1 Hybrids and beans as stable lines. But corn has also (and for a longer time, historically) been selected as 'populations' with a lot of genetic diversity that ensures it remains in good health and productivity.
Some plant species can tolerate a lot of inbreeding, that makes them genetically very similar, like when a plant pollinates itself. Not all plants are able to accept their own pollen, but some that do: lettuce, peas, beans, peppers, tomatoes. Some that (most of the time) don't: many fruit trees in the Rosaceae family (like apples). Some others need at least a little diversity (more plants in the area blooming at the same time) like Brassicas (cabbage, kale, mustards, arugula, turnips...) Alliums like onions, leeks, Umbels like carrots, parsnips, etc.
A (genetically) diverse large group of plants that pollinate each other and give another diversified group the next year, and so on.
Namely the most hated of the group, although it is by itself a necessary step in the production of almost every new OP pureline!
By definition, hybrids happen after a cross between two pure lines or varieties that present desirable traits. Like plant A is early but sets small fruits and Plant B is later to set fruit - but its fruits are extremely tasty. Hybrids combine characters and show 'hybrid vigor' in the first generation.
The following generations can be very diverse in let's say fruit size, taste and earliness. They are called F2 and so on. The drawback of the F1 hybrid is that one must perform the cross (sometimes by hand) every single year to keep selling F1s - explaining the higher cost for most F1 seeds. The advantage of the F1 hybrid: it forces the seed company to preserve two OP pure lines !...
Digging deeper in the topic
Breed your own