Meter is the poetic device that 14th century poets relied upon to make their verses easy to memorize. Another poetic device employed by them was alliteration.
In poetry, meter is a unit of rhythm, the pattern of the beats. It is also refered to as a foot. Each foot has a certain number of syllables in it, usually two or three syllables. The difference in types of meter is which syllables are accented and which are not.