Aren't we using star schemas or flocon schemas to create datamarts ? So can we say that Datamarts are synonym of star schema? Yes or no, I need justification please
No, you can't say that Data Mart is a synonym of a star schema - it is a broader concept.
Data Mart is a specialized data warehouse - it's a platform that consists of hardware, software and data.
Star Schema is a data structure optimized for querying. It's one of the components of a Data Mart, and not the only type of structures available (i.e, you can use a flat table instead).