Data or data design elements that do not conform to the rules of data normalization. Denormalized data structures are often used in databases to provide rapid access for specific user needs. Denormalization usually results in some degree of data redundancy in a data record. A process of combining like data into a single entity (table or file). This combining will create duplicate data.
(RM) Intentionally "breaking the rules" of normal forms. normalize.php
An intentional violation of the rules of normalization done to increase performance of a database. It typically occurs in varying degrees during all phases of physically implementing a database. Database designs are often denormalized to accomplish a specific performance related goal. Denormalization cannot be done without a thorough understanding of the data and the needs of the customer.