a form of a composite index

an index that includes all the columns that are referenced in the WHERE and SELECT clauses

an index, which includes all of the columns referenced in the query

a nonclustered index that contains ALL the columns referenced in any clause of a query

a non-clustered index that contains all the information requested by the user in the index's leaf level (including the key and the pointer)

a nonclustered index that is built upon all of the columns required to satisfy an SQL query, both in the selection criteria and the WHERE predicate