A relational database is a collection of data items organized as a set of formally described tables from which data can be accessed easily. A relational database is created using the relational model. The software used in a relational database is called a relational database management system (RDBMS). A relational database is the predominant choice in storing data, over other models like the hierarchical database model or the network model.
The relational database was first defined in June 1970 by Edgar Codd, of IBM's San Jose Research Laboratory.
Read more about Relational Database: Terminology, Relations or Tables, Base and Derived Relations, Constraints, Relational Operations, Normalization, Relational Database Management Systems