I've read the same material in the last week as well, wondering, why all this? Your question led me to the mathematical origins, given formal definition by an american mathematican back when there wasn't a whole lot of american mathematics happening at all: https://en.wikipedia.org/wiki/E._H._Moore#Accomplishments

It would be Veblen, his student, as well as an invading Hitler to make the likes of John van Neumann want to leave Berlin that gave the conditions for the computer to be realized. Van Neumann was effortless in the way he could take abstractions from mathematics, say, ring theory, and apply them to situations of the lowest orders of logic.

A look at the disciplines that use the term reveals that they all have their own twists, in particular because the topologists get involved: https://en.wikipedia.org/wiki/Closure_operator

For what tracks in perl, I would think that this definition is relevant: https://en.wikipedia.org/wiki/Closure_(mathematics)#Closure_operator