Gettin my first lift on this 96 XJ and got couple quesitons.

Been looking at people pics to see how high lift i want and seeing stuff like..

2.5" Rusty's & 2" BB.

Does this mean we're talking about in total a 4.5" lift? And what exactly is a BB? Maybe if i understood what this bb was i'd be able to answer my first question, just don't know enough about this stuff yet.

thanks yall