What defines a spherical triangle?

The correct answer to this question is three planes. A Spherical triangle forms from three curved arcs. It is defined as any region with three sides that are enclosed by great circle arc sides.

The angles of spherical triangles can be anywhere from 180 degrees to 540 degrees. The connecting points of the angles allow them to have sums greater than the usual 180 degrees.

Just like triangles that are in planes, a spherical triangle can have ninety degrees. Unlike Euclidean geometry, two spherical triangles are not similar. Instead, they are congruent, but only if they have the same angles.