Iambic Pentameter
Iambic pentameter is a type of poetic meter. And, to make matters a bit simpler, all of the Canterbury Tales are in iambic pentameter. Four tales, the Clerk's, Second Nun's, Prioress's, and Man of Law's, are divided into stanzas of seven lines each, with an end rhyme scheme of ABABBCC.
Rime Royal
Chaucer was responsible for originating the rime royal form in English. The fact that he uses it in the Canterbury Tales for stories with a highbrow moral and religious message, suggests that he views it as a more solemn, formal type of rhyme scheme than the rhyming couplets in which he puts much of the rest of his tales.