API for Azure Active Directory (that by the way is different than Windows Active Directory)
is called "Graph API", since data structure is graph more than a tree (directory).
But there is another Graph API by Facebook for searching Facebook data-base.
Those data are also a graph structure, so it kind-of makes sense.
To query those graph data-base, Facebook is using language GraphQL Introduction | React
But GraphDB is a third thing, and most known graph database is Neo4j,
and name GraphDB is now taken by company Ontotext that makes semantic web based software.
By the way, Neo4j founder consider semantic databases not to be graph.
The lesson from all this confusion may be that "graph data" are everywhere...
Azure Active Directory: What is the Graph API? - KuppingerCole
"AAD Graph API is the interface for navigating the content of AAD (walking the tree, or, more correctly, the graph) and accessing (and creating and manipulating) the information stored therein. Developers can perform CRUD (Create, Read, Update, Delete) operations through REST (Representational State Transfer) API endpoints"