It's a form dreamed up by Anthony Hecht and John Hollander - the Double Dactyl. The rules are as follows.
The poem consists of two stanzas, each a quatrain. The first three lines of each are formed by two dactyls, the fourth a single dactyl and a macron. The last line rhymes with the fourth. The first line is nonsense (Higgledy-Piggledy is often called into play, and is sometimes used as an alternative name for the form). The second line is a proper noun; titles are allowed (as Alfred Lord Tennyson). One of the double dactyllic lines must consist of a single word. Foreign languages are encouraged, since the inventors expressed the hope that "this will restore macaronic verse to the dignity it has not enjoyed since the middle ages".
The name - double dactyl - suggests two fingers. This is not an accident.
Here is Babette Deutsch's explanatory example;
Fiddlety-diddlety
Hecht atque Hollander,
Didacts and wits with a
Soupçon of Sade
Made of the form that the
Former invented an
UltraDraconian
Joke on the
fade.