The story
From the so-called duck test: “if it looks like a duck, swims like a duck, and quacks like a duck, then it probably is a duck.”
Etymology from Wiktionary, CC BY-SA 4.0.
duck typing
Today it means: A style of dynamic typing in which an object's current set of methods and properties determines the valid semantics, rather than its inheritance from a particular class or implementation of a specific interface. Full definition →