SQL Server Index Seek Index Scan
Index scan : The scan goes through all the row of the table whether it qualifies or not. In this scenario the cost is directly proportional to the number of rows it has to scan before it reaches its destination or its matching value.
Index Seek : The scan goes directly to the qualifying rows of a table hence the cost is proportional to the number of qualifying rows in the table.
If there is a table without an index will lead to Index Scan and with index leads to index seek.