What is the truss rod?
A truss rod is a long metal bar at the guitar neck's inner midsection that extends from the nut to the bottom. You can see them through the small hole behind the nut on most guitars. They're there to change the guitar neck relief for better playing comfort and great tone as the guitar neck naturally gets affected by lots of factors, such as variations of humidity, the tension of strings and different playing styles.
How does the truss rod work?
The guitar neck tends to bend slightly into a bow as time passes due to string strain and environment changes. The truss rod is almost like one giant string on the other side to counteract that pull and balance out the string tension.
It can be adjusted to get you the right amount of relief in the neck. Most manufacturers like a little relief, as it allows the string to vibrate freely up the neck and makes playing all over the fretboard more comfortable.
