What is the meaning of つぼ?

: a unit of areal measure, roughly 3.3m or 35.5ft, equivalent to the area of two tatami mats.

: archaic reading for modern 粒 (つぶ, tsubu), a grain, drop, or pill of something.

: a basin; a vessel or bottle; a pressure point in acupressure or acupuncture.

Source: wiktionary.org