f1 is a first generation cross between two strain (pretty sure they have to be inbred lines to officially be f1s) an s1 is a female that has been selfed which if done right will create feminised seeds and if done badly will make hermies.
When people talk about plants they say that "this plant is an f2" it has something to do with how many times the plant has been bred. Also, I have read people talking about back-crossing? This is all talked about in the context of the genetic makeup/history of a plant.
Haze- original Jamcian sativa G13-Most likely Afghani Indica. many rumors about governement programs. G13 Labs a Breeder.. and I don't think they breed the first G13 or Haze.