Here on Star Wars : Knights of the Old Republic, the back story is the setting that starts our story. We start out in an Alternate Universe in the year 3953 BBY (Before the battle of Yavin/Episode IV). The Redeemed Jedi Knight - Revan - now known as Jaden Damaracus, has defeated his former apprentice, Darth Malak, leading to the defeat of his former Empire.
We start off with the Backstory, or the plot, and from there the plot is open ended, allowing all the members to fulfill their own destinies through yet unknown means. That means that there are many stories, all going their different ways, weaving patterns into character lives.
While we have the plots of each individual character going on in the every day life, we will also continue the Factions plot, tying the story together. Many of these lives will interact with the factions of the galaxies, and those factions have their own plots which are usually dictated through their figure-head, pretty much going along with that person's or persons (plural) agenda(s) based on how their faction is run.