The "hay(na)ku" is a tercet-based poetic form invented by Eileen R. Tabios and named by Filipino-American poet Vince Gotera. The basic tercet presents the first line as one word, the second line as two words, and the third line as three words. The words can be as long or short as desired by the poet.

The "1, 2, 3" aspect of the form relates to a Filipino nursery rhyme: isa, dalawa, tatlo, ang tatay mo'y kalbo. The rhyme translates into English as "one two three, your dad is bald."

Advance words:
I find the word-based formal constraint of hay(na)ku (as opposed to a syllable or metrical foot based constraint) leads to poems that are in many ways more natural, and that, in particular, the 1-2-3 structure is a pattern that comes up continually in the course of the daily. Poetry lives and breathes in the daily, and hay(na)ku has the ability to capture profound and delightful pieces that might otherwise be missed.
-Dan Waber