The term 'Crestless Wave' can be summed up as a SWELL, which is a five-letter word. A SWELL is a large wave that has been generated by winds far away from its point of observation. Swells are usually characterized by their long period, which means they have a long time between successive wave crests. Crestless waves are swells that have lost their crests due to the effects of wind and current. They are often seen in shallow waters and can be dangerous for swimmers and boaters.