What is performance tuning?

'Performance tuning' is the term used to improve the performance of a query..that is, quickening the query execution time...a query that involves a large no of db tables may take around 20-30 min to execute for ex...

In such case, the developer shud fine tune the query and reduce the query run time..this can be done by

(i) using indexes
(ii) elimination of duplicates by using 'distinct' keyword etc..