五言 refers to a five-character poetic line and, by extension, to 五言诗 - verse in which each line has five syllables. The form crystallised in the Han-dynasty 古诗十九首 and dominated early classical poetry before 七言 took over.
usage
Pairs with 七言 (seven-character). The two together describe almost all regulated Tang verse: 五言绝句, 七言绝句, 五言律诗, 七言律诗.
