A clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore, the table can have only one clustered index. The leaf nodes of a clustered index contain the actual data.

A non-clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows on the disk. The leaf node of a non-clustered index does not consist of the data pages. Instead, the leaf nodes contain index rows and a pointer to data (Clustered Index key or RID).