Each Non-clustered table has a data segment. All of the tables data is stored in the extents of its data segment. Each cluster has a data segment. The data of every table in the cluster
Each Index has an Index segment that stores all of its data.
A Database contains one or more Rollback Segments to temporarily store "undo" information.
Rollback Segments are used : To generate read-consistent database information during database recovery to rollback uncommitted transactions for users.
Temporary segments are created by ORACLE when a SQL statement needs a temporary work area to complete execution. When the statement finishes execution, the temporary segment extents are released to the system for future use.