No, you haven't stumbled upon Italian Shmoop (although we can do a mean Florentine accent). Ottava rima is just the term used to describe a poetic form whose stanzas have eight lines (ottava) and follow an ABABABCC rhyme scheme.
As you might have guessed, ottava rima got its start in Italy, probably in the 14th century from Giovanni Boccaccio, the guy who wrote the awesomely hilarious and kind of obscene Decameron. The form then had its heyday in the European Renaissance epic, with authors like Ludovico Ariosto, Torquato Tasso, and Luís de Camões making those octaves shine.
We're pretty used to reading this form in epics, but our buddy Yeats decided to throw us a curveball—he wrote the definitely-not-epic poem "The Circus Animals' Desertion" in ottava rima. Check it out, and let it surprise you.