Recursion
Etymology
From Latin recurrere, "to run back" (re-, "back," plus currere, "to run"). Mathematicians and logicians developed the modern sense in the early twentieth century, and it became foundational in computer science: a function that calls itself. The key discipline is the "base case" that keeps it from running forever.
noun · /rih-KUR-zhun/
A process defined in terms of itself, where each step repeats the same rule on a smaller piece until it reaches a case simple enough to stop.
What it names
The pattern behind anything that contains a smaller copy of itself — nested folders, a story within a story, or a plan that keeps applying to its own results.
Example
Explaining the joke required explaining the earlier joke it referred to, which was itself about a still older joke — a small recursion that never quite bottomed out.
Related idea
Recursion repeats a rule on ever-smaller versions of the same problem; a fractal is the visible shape that endless recursion produces — self-similar at every scale.