Metrical writing is poetry — or song words — built with a pattern of strong and weak beats, like a drum you can tap. In English we often feel this as da-DUM da-DUM, or another regular pattern. A metrical line has that beat on purpose; free verse does not. Teachers call the study of these beats metre (American spelling meter). You will see metrical in literature class far more than in the street. Hymns and older poems are often metrical; many modern poems are not. Though actually, this word is easy to mix with metric, the system of metres and kilograms. Metrical here has nothing to do with measuring a table. It is about the counted rhythm inside a line, not about science class.