Hand evaluation, Rule of Protective bidding
First read about balancing here, where the 4th player bids after 2 passes.Rule of 15
This is a secondary hand evaluation system used by some people when the 4th seat does not have sufficient strength to open after 3 passes, using a traditional point count.
Count the traditional High Card Points and then add 1 point for each Spade. If the cumulative value is 15 or greater, open the bidding.