A programming technique where a function calls itself to solve a problem by breaking it down into smaller, similar subproblems. Each recursive call works on a simpler version until reaching a base case that stops the recursion.
From Latin 'recurrere' meaning 'to run back,' from 're-' (back) + 'currere' (to run). The mathematical concept existed for centuries, but the programming term was formalized in the 1960s when computer scientists realized functions could 'run back' to themselves.
Recursion is like Russian nesting dolls (matryoshka) - to open the big doll, you open it and find a smaller doll inside, then you open that smaller doll the same way, and keep going until you reach the tiniest doll that can't be opened further. Each step is the same process, just on a smaller scale!
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