A coronagraph is a feature or attachment for a telescope designed to block light from a bright object in view so that other objects can be seen more clearly. Originally designed to view the Sun's corona, versions are now used to block star light, for example, direct imaging of extra-solar planets. Coronagraphy is astronomy, e.g., observation, making use of coronagraphs. In this case, inner working angle refers to the smallest angle between the planet and the star, as seen from the telescope, at which the planet can be detected.
The terms occulter and coronagraph are sometimes used like synonyms and other times, the part of the coronagraph actually blocking the light is called the occulter. The word occulter also is used for starshades and for the bodies that occult in occultations.