Slot

The gap through which air flows between two adjacent sails.

The term most commonly describes the space between a headsail and mainsail. Its width and shape change with sail trim, sheet lead, mast position and the relative sizes of the sails.

Airflow through the slot influences the pressure distribution and flow over both sails. A slot that is too narrow can disturb or backwind the mainsail, while an excessively open slot may indicate inefficient trim; the useful appearance depends on sail design and point of sail rather than one universal gap.