What is mean by Dimensional Data Modeling?

Dimensional data model is most often used in data warehousing systems.

In Datawarehouse, a schema is used to define the way to organize the system with all the database entities (fact and dimension tables) and their logical association.

In designing data models for data warehouses / data marts, the most commonly used schema types are as below :

Star Schema :

A fact table in the center surrounded by multiple dimension tables.

Snowflake Schema :

A fact table in the center surrounded by multiple hierarchies of dimension tables.

Galaxy Shema / Fact Constellation Schema  :

Multiple fact tables share the same dimension tables. The arrangement of fact tables and dimension tables looks like a collection of stars in the Galaxy schema model.

Star Cluster Schema :

Combination of Star and Snowflake schema.

Whether one uses a star or a snowflake largely depends on business needs.