Video narration
At twelve and three on a clock, the hands make a quarter-turn. Move them closer, and the opening shrinks; point one hand to six, and they make a half-turn. That opening is an angle: the amount of turn between two lines meeting at one point. An opening greater than zero but less than 90 degrees is an acute angle. Exactly 90 degrees, a quarter-turn, is a right angle. More than 90 but less than 180 is an obtuse angle. Exactly 180 degrees, a half-turn, is a straight angle. To classify any angle, measure its turn and compare it with 90 and 180. A full turn around the clock is 360. Here's the flip: the name comes from the measured turn, not whether it looks narrow or wide. Under 90 is acute, 90 is right, between 90 and 180 is obtuse, and 180 is straight.