There are two main types of angles: acute (<90°) and obtuse (>90°). (There are also straight, right, zero and full angles but that is not the discussion here 
Acute angles, called here interior are more difficult to finish (files even small cannot easily fit in the angle and remove material, they are obstrusive).
Obtuse angles give a much easier access for tooling like files, and can be finished easily.
The wording anglage, interior and exterior must be derived and translated from Horological Swiss French.
Best,
E.