井 means 'well'

As these essays amply demonstrate, squares delineate much of life in Japan. Two tatami mats placed side by side form a square, and those squares (坪) constitute units of measurements, whether of floor space or land area. Ceilings traditionally have lattice patterns. Students write in squares on grid paper. People drink saké from wooden masu boxes. Japanese wells are typically square, and the shape of a well ledge has inspired all kinds of hashtag-like designs from famous corporate logos to family crests to fabric patterns. These essays will have you thinking inside the box!