Step 1: Unpack what the name NoSQL is contrasting itself with.
NoSQL exists as a category precisely to describe databases that step away from the traditional table based, SQL driven relational approach, so it helps to first ask, what is the one model that NoSQL is defined in opposition to.
Step 2: List the genuine NoSQL families.
Document based databases like MongoDB store JSON like documents, key value stores like Redis pair simple keys with values, graph based databases like Neo4j store nodes and edges to represent relationships, and column family stores like Cassandra organise data in wide columns, all four of these deliberately avoid the rigid table and join structure of SQL.
Step 3: Recognise the model that does not belong.
The relational model, with its predefined schema, tables of rows and columns, and SQL query language, is exactly the traditional approach that NoSQL databases were built to move away from, so by definition it cannot itself be classified as a type of NoSQL database.
Step 4: Conclude.
The option that is not a NoSQL database type is
\[ \boxed{\text{Relational}} \]