A MASU was originally a square wooden box used to measure rice in Japan, today MASU are largely used for drinking sake.

Japanese Masu Wooden Sake Cups with Kanji Happiness Engraved
Our Wooden Masu are Made out of hinoki wood-Japanese Cypress, Will not Leak. Measures 3.25 inches Square and 2.25 inches Height, Holds 4 ounce sake.
Wooden sake box are great for chilled sake, served with a saucer to catch dripping. Also serve sake with glass sake cup inside the wooden masu. fill the glass cup until it overflows into the wooden masu box.
Wash wooden saki cups only with running water. Do not use hot water either a dishwasher.
Made in Japan with High Quality

MPN: OMS-103
UPC: 4539429508041