The enclosure of one loop, block, etc. of code inside another.(noun)
Wiktionary.org : Text is available under the Creative Commons Attribution-ShareAlike License
Use "nesting" in a sentence
"But I prefer the term nesting rhymes because the words nest one inside the other like Russian wooden dolls."
"Wane not though, my dear, for we definitely will return too a city I now understand why nesting is inevitable."
"This model possesses an implicit temporal dimension because the nesting is based on the relative recency of common ancestry, but it lacks a horizontal dimension of time."