anapest (n.) – a metric foot composed of two short syllables followed by a long one, as in the word seventeen
“You can’t say, ‘Where’s it?’ So the choice is between ‘Where is it?’ and ‘Where’s it at?’, and the latter, a strong anapest, is prettier and trips off the tongue better.”+
Wallace, David Foster. “Authority and American Usage.” Consider the Lobster. New York: Back Bay Books, 2007. p 99.