If the poet has bread and butter, it is meter.

Prosody is a linguistic term that in its relationship with poetry describes the study of the mechanics of verse. It is commonly separated into three sections- isochrony, intonation and stress. Of these three, isochrony is the most critical for the written word. It is the postulated (or claimed) rhythmic division of time into equal portions by language.

Or in other words… meter.