The difference is that, Clustered index is unique for any
given table and we can have only one clustered index on a
table. The leaf level of a clustered index is the actual
data and the data is resorted in case of clustered index.
Whereas in case of non-clustered index the leaf level is
actually a pointer to the data in rows so we can have as
many non-clustered indexes as we can on the db.