The story
The necessity of such a boundary term was first realised by James W. York and later refined in a minor way by Gary Gibbons and Stephen Hawking.
Etymology from Wiktionary, CC BY-SA 4.0.
Gibbons-Hawking-York boundary term
Today it means: In general relativity, a term that needs to be added to the Einstein-Hilbert action when the underlying spacetime manifold has a boundary. Full definition →