Database systems use a network model to store their data in a graph. Much like the Hierarchical database model, the nodes of the graph contain information. The information is stored in a graph, so one parent can have many children, and one child can relate to several parents. The model is also known as CODASYL model, because it was originally proposed by the CODASYL consortium (who also developed COBOL).
In a network model, the defining feature is that each record has a link to another record.