S, SF, MOS,....Can someone explain?

So, I am considering a Glock in 45...

I love my 26, its old though, and I want a 45, I do have a Gold Cup in 45 but I want something different...

So, I went to Glock.com and was useing their compare feature. Nowhere on the site could I find an explanation of the differences between S, SF, Gen 4, MOS...

I believe the gen 4 has a rail and the MOS is some kind of modular system for sights and grips?

What is the S and SF?

Forgive me my ignorance, I am not the best internet searcher...