Normalization is a process in SQL where we remove redundancy from the data for enhanced data integrity. It helps in organizing the data in the database and ensures that the data integrity constraints are appropriately executed with their dependencies. Normalization is a systematic technique of decomposing tables to eliminate data redundancy and undesirable characteristics like Insertion, Update, and Deletion anomalies.

Normalization rules divide larger tables into smaller tables and link them using relationships. The purpose of normalization in SQL is to eliminate redundant (repetitive) data and ensure data is stored logically. The database normalization process is further categorized into the following types:

• First Normal Form (1NF)
• Second Normal Form (2NF)
• Third Normal Form (3NF)
• Boyce Codd Normal Form or Fourth Normal Form (BCNF or 4NF)
• Fifth Normal Form (5NF)
• Sixth Normal Form (6NF)

The first three forms of normalization are the most commonly used and are considered the highest level necessary for most applications. A database is considered to be in third normal form if it meets the requirements of the first three rules.

In summary, normalization is a way of organizing the data in the database to ensure that database integrity constraints properly execute their dependencies. It is a multi-step process that sets the data into tabular form and removes the duplicated data from the relational tables. The purpose of normalization in SQL is to eliminate redundant data and ensure data is stored logically.