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Roll
If you tilt your head to read the spine of a book, this is roll in action. One of the three rotational axes commonly used to describe the rotation of an object. The term comes from aviation. Most RT3D engines count from -180 to 180 degrees, starting out rolled upside-down all the way to the left, turning clockwise and ending up rolled upside-down all the way to the right. Straight forward with no roll is 0 degrees. See also pitch, yaw, rotational axis.