i was recently out playing in my dd jeep on the some sand bars in a river its not anything fance 2.5" lift and as of today 33s but someone i was with said i need to get lockers and that would help me through the sand so my question is what exactly are lockers and what would be best to get for someone on a tight budget and for my dd weekend warrior?

 

Use search function. This will get you started.

http://en.wikipedia.org/wiki/Locking_differential
There are several types varying greatly in price that we can use on the XJ. Pretty easy to find info about them