What is the billowing sail let out sometimes from the front of yachts?

The billowing sail let out from the front of yachts is called a headsail or jib. It is used to catch the wind and help propel the yacht forward, often working in conjunction with the mainsail. The headsail can be adjusted in size and shape to optimize performance based on wind conditions. Common types of headsails include the genoa and the storm jib.