Table Scan
SQL processes all rows in the table looking for a match
Index Scan
SQL processes all rows in the index looking for a match
Index Seek
SQL processes the leaf layers and leaf nodes looking for a match
Index seek is normally the most efficient but depends on indexes and data volumn. If sql determines that the query would be too costly for a seek it may revert to an Index or Table scan.
Hope this helps.
Far away is close at hand in the images of elsewhere.
Anon.