Hi Saurabh,
As Venkat explained, there are various Schemas in HANA, i just want to add a couple of things,
SYS - this schema generally contains all your System Views and System Tables: To know more about them, check this
http://help.sap.com/hana/html/SAP_HANA_SQL_and_System_Views_References_en/2e/1ef8b4f4554739959886e55d4c127b/frameset.htmhttp://help.sap.com/hana/SAP_HANA_Database_System_Views_Reference_en.pdf
_SYS_REPO - there is a System User in HANA called _SYS_REPO and it has its own schema as _SYS_REPO. This schema is used by designer component of HANA Studio during the activation of Objects. All the Objects that you will create in HANA Development Perspective are owned by User _SYS_REPO.
_SYS_BI - "All the BI related tables get stored hear." This is not the correct answer - This schema stores all the metadata of created column Views.
_SYS_BIC - As explained above all Column Views are stored here.
_SYS_XS - not SYS_XS-ENGINE - as explained above is used for Extended Application Services
_SYS_STATISTICS - contains the Statistics data of the Statistics Server
_SYS_RT - i don't know exactly, but from seeing tables i guess its used for CDS, UIS and Text Search
UIS - This schema is used for UIS purposes.
Regards,
Vivek