The **Angle** between two [[Line, Line-Segment, Ray|ray]] with a shared vertex is the length of the [[Arc|arc]] of the [[‡ Unit Circle|unit circle]] centered at the vertex of the rays. This measurement will be in [[‡ Radians]], so to convert to [[‡ Degrees]], the arc length should be multiplied by $\frac{180\degree}{\pi}$ Angles can be signed ### Individual angles There is some common terminology for angles, whose measure is always non-negative (see [§ Signed angles](https://en.wikipedia.org/wiki/Angle#Signed_angles)): - An angle equal to 0° or not turned is called a [[zero angle]]. - An angle smaller than a right angle (less than 90°) is called an [[acute angle]]. - An angle equal to 1/4 turn (90° or π/2 radians) is called a _[right angle](https://en.wikipedia.org/wiki/Right_angle "Right angle")_. Two lines that form a right angle are said to be _[normal](https://en.wikipedia.org/wiki/Normal_(geometry) "Normal (geometry)")_, _[orthogonal](https://en.wikipedia.org/wiki/Orthogonality "Orthogonality")_, or _[perpendicular](https://en.wikipedia.org/wiki/Perpendicular "Perpendicular")_. - An angle larger than a right angle and smaller than a straight angle (between 90° and 180°) is called an _obtuse angle_ ("obtuse" meaning "blunt"). - An angle equal to 1/2 turn (180° or π radians) is called a _straight angle_. - An angle larger than a straight angle but less than 1 turn (between 180° and 360°) is called a _reflex angle_. - An angle equal to 1 turn (360° or 2π radians) is called a _full angle_, _complete angle_, _round angle_ or _perigon_. - An angle that is not a multiple of a right angle is called an _oblique angle_.