what is fully-fledged promise
That means that the values returned by queries are thenables per the definition of the Promises/A+ spec, but not actual Promise
instances. That means they may not have all of the features of promises (for instance, catch
and finally
methods). Actual Promise
instances would be "fully-fledged" promises.
The English term "fully-fledged" means "complete" or "fully developed." It comes from ornithology (or at least, terminology related to birds): A chick (a young bird) that has its adult feathers is "fledged;" if it has all its adult feathers completely covering its down undercoat, it's fully-fledged.