Lafazin “head Sea” yana nufin kalmar ruwa da ake amfani da ita wajen siffanta yanayin igiyar ruwa da igiyoyin ruwa ke zuwa gaban jirgin kai tsaye, watau a sabanin tafiyarsa. Mahimmanci, tekun kai wani yanayi ne wanda jirgi ke motsawa a kan halin yanzu ko raƙuman ruwa. Hakanan za'a iya amfani da kalmar ta misali don bayyana duk wani yanayi da wani ke fuskantar matsaloli ko cikas gaba-gaba.