The OGC Architecture Board has been trying to define the term "convenience API". I pointed them to the description in https://www.w3.org/TR/sdw-bp/#convenience-apis. This could be the basis of their definition, but it seemed from the discussion I had with them that they were looking for a somewhat less narrow definition.

I re-read the BP myself and think that the descriptions under Why and Intended outcome provide good input for a definition.

Some key quotes from the BP:

tailored to meet a specific goal; enabling a user to engage with complex data structures using (a set of) simple queries

provides a coherent set of queries and operations, including spatial ones, that help users get working with the data quickly to achieve common tasks. The API provides both machine readable data and human readable HTML markup. The human-readable markup will also support search engine's Web crawlers to enable indexing of spatial data.

... And there's more under Possible approach for implementation, although these are perhaps too specific for a definition - they are more like suggestions on how to make a spatial data API convenient:

well documented and easy to understand, both in terms of the options to access / filter the data and of the data structures that are returned

Return data in chunks fit for use in Web applications and as useful sets of information.

simplifying the geometries

overly small pieces of data are inconvenient to use

Support queries for Spatial Things based on user needs

Do we still think all these are aspects of (spatial) convenience APIs? Is there more?