The phrase "calm seas" means that the water in a body of water, like an ocean or lake, is still and peaceful without any waves or storms. Full definition
These towering, solitary walls of water can measure tens of meters in height and are difficult to predict, often occurring in calm seas with little warning. (sciencemag.org)
Enjoy a relaxed breakfast while soaking - in at the serenity spread all along the beaches or listen to the sound of calm sea waves while enjoying leisure walk during sunset. (indianholiday.com)
Your arms reach straight across toward your knees, parallel to the floor, like the deck of a ship on calm seas. (yogajournal.com)