Traditionally a coronagraph is something that blocks the bright disk of our Sun to make it easier to image the much dimmer corona. The first coronagraph is of course the Moon; during a solar eclipse it blocks the Sun and those who cautiously glance up at it during totality can see the corona.
Schemes to directly image exoplanet systems usually (always?) need at least some coronagraph-like functionality to block the star's light in order to image the planets that orbit it.
This usually happens within the telescope, often at an intermediate focal plane.
But space telescopes offer the possibility of the old-fashioned eclipsing coronagraph. The same way that our Moon just nicely blocks our Sun, and independent spacecraft several to several thousand kilometers away from a space telescope could eclipse the disk of another star, allowing for imaging of the exoplanet system around it.
Question: What will (likely) be the first separately-orbiting coronagraph to be deployed in space?
For an example of advanced coronagraphs integral to space telescopes, see
- Why is the Nancy Grace Roman Space Telescope (WFIRST) coronagraph considered “(beyond-)state-of-the-art”?
- How could a 20 inch space telescope “be able to make out Earth-size planets” orbiting Alpha Centauri?
For an example of a separate coronagraph or "star shade", see
- How do HabEx's internal coronagraph and external starshade work together and complement each other? What is it that each can do that the other can't?
Results of a conventional coronagraph integrated within a space telescope, from How (the heck) does SOHO's SWAN camera image the entire 4π sr celestial sphere?
screenshot from 4 Future Space Telescopes NASA wants to build