sixty tortillas, pieces of paper, cloths, mats, or similar things (flat and thin)
Alonso de Molina:
yeipilli. sesenta tortillas, pliegos de papel, mantas esteras, o cosas semejantes. Alonso de Molina, Vocabulario en lengua castellana y mexicana y mexicana y castellana, 1571, part 2, Nahuatl to Spanish, f. 35r. col. 2. Thanks to Joe Campbell for providing the transcription.
Attestations from sources in English:
The construction is 3 x 20 = 60, where ipilli means 20.