The cavity or channel within a tube or tubular organ.
In the International System of Units, the derived unit of luminous flux; the light that is emitted in a solid angle of one steradian from a source of one candela. Symbol: lm.
The cavity bounded by a plant cell wall.
The bore of a tube such as a hollow needle or catheter.
A small opening or orifice, as in a body organ or passage.
Any of the small openings or pores in a sponge.
The mouth of a river.