Bay/beɪ/ Definition 1 of 5Pro Tip 1/3Body of Water Remember 'bay' specifies a body of water; don't confuse it with land formations. We sailed into the bay, leaving the rough ocean waters behind. Pro Tip 2/3Partly Enclosed A 'bay' is not fully enclosed by land; one side is open to the sea or lake. The bay opened up to the horizon, its waters blending with the sky. Pro Tip 3/3Geographic Names 'Bay' can be part of a place name, related to geographic features. San Francisco is famous for its Golden Gate Bridge and the Bay Area.