The term 'sonnet line quintet' refers to a group of five lines in a sonnet, which is a type of poem that originated in Italy during the Renaissance. The five lines are usually written in iambic pentameter, which is a poetic meter consisting of five pairs of syllables, with the second syllable of each pair being stressed. The five lines are often referred to as an iambic pentameter, or an iamb, which is a five-letter word.