github.com/facebook/prop-types is the 2nd google search result for this term, and is what I was referring to, although the first result (devhints.io/react#property-validation) is arguably a better summary.

Ie. ‘lite’ type checking, used in react.

(did you perhaps see the results for ‘javascript prop type hint’ as a google autocorrect suggestion or something? This is a well known term, but I’m pretty amazed two seconds of google didn’t discover what it was...)