We will be removing all instances of the term "Entities" from the Java / REST API codebase. An "Entity" is not an actual object in DSpace 7, as all Entities are represented as Item objects. So, within the codebase, the term Entity will not be used as it is synonymous with Item. Essentially, the feature can even be called "Configurable Items".
See this PR comment for further details: https://github.com/DSpace/DSpace/pull/2246#pullrequestreview-175007207
(This ticket will be worked on by the DSpace Entities Working Group, and is just in Jira for tracking purposes)