It means relative to the meter. It also means that it can be measured. Relating to measures. Measure. In literature it is the number of syllables that a verse has, but applying special rules.
1º_ Feminine of metric ("relative to the meter or the measure" ) . 2º_ In poetry it is the art of measuring and combining the verses. 3º_ In language and phonology is the study of the characteristics of the tunes and accents in each language.