Definition:Inner Angle of Spherical Triangle

Definition
Let $\triangle ABC$ be a spherical triangle on the surface of a sphere whose center is $O$.

Let the sides $a, b, c$ of $\triangle ABC$ be measured by the angles subtended at $O$, where $a, b, c$ are opposite $A, B, C$ respectively.

Consider the $4$ consecutive parts of $\triangle ABC$:
 * $B, a, C, b$

Then $C$ is known as the inner angle of $B, a, C, b$

Also see

 * Definition:Inner Side of Spherical Triangle