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 GameEngines|game 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.