A positive angle is convex if it is at most 180 degrees, i.e. $\pi$ radians. Cf. the convex set.

A convex angle $\alpha$ is

• straight if $\alpha = 180^{\mathrm{o}}$ ,
• obtuse if $90^{\mathrm{o}} < \alpha < 180^{\mathrm{o}}$ ,
• right if $\alpha = 90^{\mathrm{o}}$ ,
• acute if $0^{\mathrm{o}} < \alpha < 90^{\mathrm{o}}$ ,
• skew if it is acute or obtuse.

Note. The angle between two curves which intersect each other in a point $P$ means the angle between the tangent lines of the curves in $P$ ; such an angle may always be chosen acute or right.