“Open” is one of the most overloaded words in this field, and the ambiguity is frequently doing work for somebody.
It can mean publicly documented — anyone can read how it works. It can mean publicly accessible — anyone can sign up and call it. It can mean free of charge. It can mean openly licensed, so the interface design and schema can be reimplemented. It can mean open source, referring to an implementation. It can mean governed in the open, like OpenAPI under the OpenAPI Initiative. Or it can mean nothing at all beyond marketing, as in “we are an open platform” attached to an API with an approval queue and terms that forbid competition.
These are wildly different commitments. An API that is publicly documented but requires a partnership agreement to call is open in one sense and closed in every sense that matters to a developer.
So when you hear it, ask which one. And when you say it, be specific — say publicly available, or openly licensed, or free tier available, or open governance. Precision here is not pedantry; it is the difference between a promise and a vibe.
