Neo4j is a graph database management system
Neo4j is a graph database management system (GDBMS) developed by Neo4j Inc.
The data elements Neo4j stores are nodes, edges connecting them, and attributes of nodes and edges. Described by its developers as an ACID-compliant transactional database with native graph storage and processing, Neo4j is available in a non-open-source "community edition" licensed with a modification of the GNU General Public License, with online backup and high availability extensions licensed under a closed-source commercial license. Neo also licenses Neo4j with these extensions under closed-source commercial terms.
Neo4j is implemented in Java and accessible from software written in other languages using the Cypher query language through a transactional HTTP endpoint, or through the binary "Bolt" protocol. The "4j" in Neo4j is a reference to its being built in Java, however is now largely viewed as an anachronism.
Neo4j is a graph database management system. It is highly flexible, highly scalable, and uses the Cypher query language to take advantage of its graph-based method of structuring data.