whats the difference between SR5,TRD,Prerunner...?

I'm a 1st generation 4 banger so i don't need to know about the TRD off-road and sports. But i have been wondering for awhile what the SR5 stood for and what a prerunner is? My truck has SR5 emblems on it an it has the TRD package, but i don't know what either of them added to the truck, this is my first tacoma and i bought it used so i couldn't really compare it.

 

A "Prerunner" is a 4x2 with the 4x4 ride height and suspension. I've always wondered what "SR5" means too. I heard along time ago that "SR5" meant Safety Rating=5, but haven't confirmed this. ???

 

The TRD refers to the offroad package, that usually comes with stiffer Bilstien shock absorbers, and in most cases, a rear differential locker.

I don't think the TRD 2.7l's ever came with the diff locks, since I have a TRD with no diff lock.

I thought the SR5 was like the accessory package or whatnot. I have power locks, windows, remote entry, and a security system...I always supposed that's what SR5 was.

 

My truck has the power everything also, so maybe that is what the SR5 is.. i have a locking rear diff with my TRD package, i had always thought that it was apart of that?
Thanks for the replies, i atleast now know for sure waht a prerunner is.