For many philosophers, the scholarly debate around holes began in earnest in 1970, with Lewis and Lewis’s now classic article for the Australasian Journal of Philosophy (48: 206–212.)
The authors presented their paper in a highly unusual format - that of an imaginary discussion between two philosophers, called Argle and Bargle, who are pondering the holes in a piece of Gruyère cheese.
Argle believes that every hole has a hole-lining, and therefore the hole-lining is the hole. On the other hand, Bargle points out that even if hole-linings surround holes, things don’t surround themselves.
The answers are still not clearcut, but since the 70’s the philosophical debate around holes has continued and expanded considerably, and there is a suggestion that they could perhaps be categorised as a subsection of 'Almost Nothings' which also include cracks and shadows.
See:‘Being and Almost Nothingness’ in the journal Noûs, Volume 44, Issue 4, pages 628–649, December 2010.
Also see: Where Argle and Bargle got things wrong, by Cargle and Dargle Australasian Journal of Philosophy 82:1 (2004), 23–2.