API Data Book meaning in oil and gas

The term API is usually used to describe already-created (i.e. 'tinned') routines that can be called to perform known functions and/or return specific values. APIs often act as the interface between a complex existing code or application layer and new code or user interfaces that are being built onto it. An API Data Book? A kind of glossary defining what data and values you can feed into a specific set of APIs and what you could expect as a result.