The degree is properly referred to as an arc degree, or a degree of arc. It is a measurement of angle (1/360th of a full rotation) and although not an official SI unit it is an accepted SI unit.
A division of a circle, equal to 1/360 of its circumference.
History doesn't record who first decided to subdivide a circle into 360 degrees and how this number was chosen. It seems likely that it was chosen due to it's closeness to the number of days in a year, and because it has an unusually large number of numbers by which it can be divided. Timocharis of Alexandria is credited as one of the first Greeks to use 360 degrees and he lived between 320 and 260 BC. Before that, the Rigveda mentions a wheel divided into 360 pegs. The Rigveda was written somewhen between 1500 and 1200 BC.
- There are 90 degrees in a right angle, and 180 degress in an about turn. If you put your index and middle finger in a 'V' shape, they make an angle of approx. 45 degrees.
The degree is the most commonly used angular measurement unit
- A degree can be subdivided into 60 minutes. Each of those minutes can be further subdivided into 60 seconds
- There are 360 degrees in a circle.