RESTful APIs can be internal (your company’s only) or public facing (Twitter). Thus internal APIs are called “Private APIs” and open to the public APIs are called “Open APIs”
Now, while building an API accelerator for our clients I was asked by a well meaning colleague if this was an Open API; the intent was right but there was a subtle error in the language semantics. I believe what he meant was “did you write the API using Open API Specification” and not “is this API open to the world wide web?”
Open API specification or OAS is derived from Swagger and the de-facto standard for writing APIs. You can write public facing or internal APIs with OAS. Simply picking this style does not make your API open to the public i.e. you need to host this API on a public portal to make your Open API Specification based API Open to the public
Summary
Just because I wrote my APIs using RAML (the other standard) does not make it closed or non-standard. The Open API Specification is a good standard and you can convert from RAML to OAS
It is important to write an API specification and do it well regardless of the specification language
Alok Mishra 