The truss rod is a metal rod that runs down the inside of the guitar neck it counteracts the pressure of the strings pulling the neck forward.
Truss rod repairs are fairly uncommon but when they become over tightened they do stand the chance of stripping the thread on the rod.
This is why you should always leave the adjustment of your truss rod to a trained professional.
Below you will find links that will take you forwards to pages detailing the repairs to truss rods.