If measured on the inside of the polygon, the it is an interior angle.
It meets all definitions I can find, and it would seem that a straight angle can be adjacent. Definition: (1) Two angles that share a common side and a common vertex, but do not overlap. (2) An adjacent angle is either of two angles having a common side and a common vertex. Adjacent angles are angles that have a common ray coming out of the vertex going between two other rays. Another way of saying this is that adjacent angles are next to one another, side by side or adjacent. (Hence the name) It is an angle next to another one in a polygon.
a triangle
A decagon
I think it is adjacent
triangel
A Regular Polygon
It meets all definitions I can find, and it would seem that a straight angle can be adjacent. Definition: (1) Two angles that share a common side and a common vertex, but do not overlap. (2) An adjacent angle is either of two angles having a common side and a common vertex. Adjacent angles are angles that have a common ray coming out of the vertex going between two other rays. Another way of saying this is that adjacent angles are next to one another, side by side or adjacent. (Hence the name) It is an angle next to another one in a polygon.
It is an irregular polygon
A six-sided polygon. It also has the special name hexagon.
A decagon
a triangle
The name of a 20 sided polygon is Icosagon.
An irregular polygon.
octagon
I think it is adjacent
That is called a regular polygon.
triangel