什么叫八音节对偶诗？

A poem having eight syllables in each line.
一首每行有八个音节的诗
a verse line having eight syllables or a poem of octosyllabic lines.
诗中每行有八个音节。
The lengthening of a normally short syllable in Greek and Latin verse.
（诗的）音节拉长希腊文和拉丁文诗句中通常短音节的延长
A line of verse consisting of eight metrical feet.
八音步诗句有八个诗步的诗行
A group of eight lines of poetry, especially the first eight lines of a Petrarchan sonnet.
前八行诗诗歌中一组八行，尤指彼得拉克十四行诗中的前八行

对偶是将字数相等、结构相同或相似的两个词组或句子成对地排列起来的修辞法。
具体参看http://baike.baidu.com/view/632018.htm