The first corona of a tile is the set of all tiles that have a common boundary point with that tile (including the original tile itself). The second corona is the set of tiles that share a point with something in the first corona, and so on.
Four of the Johnson solids are also known as coronas.
More things to try:
Weisstein, Eric W. "Corona." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Corona.html
