To put it simply, it is to place your left hand in the twelve position, and the right hand to play the string, and the sound produced is twelve tones.
The twelve is very special on the guitar. Because according to the twelve average law, the pitch of twelve is exactly eight degrees apart from the empty chord, which is an extremely concordant interval. Therefore, the solo usually starts from twelve, and the twelve is the most important 1/2 pan point of the guitar. The overtones are most bright here.