RADIANS

The other method of specifying fractions of an ac cycle is to divide it into exactly 2π, or approximately 6.2832, equal parts. This is the number of radii of a circle that can be laid end to end around the circumference. One radian, symbolized rad (although you can write out the whole word), is equal to about 57.296°. Physicists use the radian more often than the degree when talking about fractional parts of an ac cycle.
Sometimes the frequency of an ac wave is measured in radians per second (rad/s) rather than in hertz (cycles per second). Because there are 2π radians in a complete cycle of 360°, the angular frequency of a wave, in radians per second, is equal to 2π times the frequency in hertz. Angular frequency is symbolized by the lowercase italicized Greek letter omega (ω).