exterior angle
Noun
Meaning
the supplement of an interior angle of a polygon
Source: WordNetSynonyms
external angle
coin
coign
acute angle
central angle
adjacent angle
complementary angle
corresponding angle
bisexual angle
alternate angle
outside viewpoint
bisector angle
congruent angle
front angle
exterior corners
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Examples
Even in a non-simple polygon it may be possible to define the exterior angle, but one will have to pick an orientation of the plane (or surface ) to decide the sign of the exterior angle measure.
The exterior angle here could be called a supplementary exterior angle.