Definition: In the Seemiller grip, the racket is held similarly to the shakehand grip, but with a 90 degree turn so that the thumb and index finger are used to grip the sides of the bat. Both forehand and backhand are played with the same side of the bat, although the bat can be turned to use the other side. It is typically used with a combination bat.
This grip is named after Dan Seemiller, who first popularized the grip in the 1970’s, and enjoyed world level success with it. I have a more detailed explanation of the Seemiller grip (with photographs) on the site here.
Also Known As: windshield wiper grip