S1 are seeds that have 1 plant reversed and pollinated to itself, or a direct clone pollinated of itself. It is how a breeder copies a clone only cut. It is litterally a copy of itself in seed form and the seeds are very same and uniform.
F5 are seeds that have been selected out 5 generations and re bred. The first generation of crossing two dissimilar strains we refer to as F1. And so forth down to F5. Most cannabis starts to become infertile around F6 to F7 generation so few go past F5 generation. Each round a boy and a girl are selected from growing out the F(x) generation seeds and selecting for the two or three that are most like mom. Till f5 is reached and you have homogenized the traits into very “like clone” seed stock.
Inversely, f1 generation are wildly all over the place. They open the gene pool so you get some like mom, some like dad, and some like grandma, and some like grandpa. F5 should all be narrowed down to copies of mom.
IBL stands for inbred line. It’s where any combo of these breeding practices are used to make uniform growth traits of the seeds. A breeder could use both f5 generation and a clone of mom, then self mom and pollinate the f5. Select and regrow always for uniformity. It becomes an inbred line. The quinesential example of this in my opinion is a landrace strain. So inbred for its characteristics it’s a distinct plant “culture”. Had to steal a term from humans.
Most breeders list on each seed description what generation they are so you know what to expect. If I get F1s I get a mixed bag of roughly familiar traits. If I get f5 they should look like clones. Ditto for S1 or anything IBL listed in descriptor.
Interestingly, ILGM has in the few autos and regs I read descriptions for, nothing about the generation. I don’t know what to say about that. Either way it’s good to know this.
Is there a standard practice ILGM goes too?
Or a breeder could start with a F1 gen and see something wild and crazy nothing like mom. Literally a good distraction. Take that weird F1, self it (s1), and start a whole new line essentially removing the original mother and inbreeding for the new original weird trait that distractingly caught your eye. 