What does the "F" stand for in animation

The "F" stands for "field". The field refers to what the camera will see when the page is shot under the camera. A field guide is used to mark the size of the shot. So When you order 10f size you are ordering a 8 1/2" x 11" size of paper. The 12f is 10 1/2" x 12 1/2" and a 16f is 12"x 17".