1. Any of various small openings or pores in an animal body, especially an opening resembling a mouth in various invertebrates.

2. Botany: A minute pore in the epidermis of the leaf or stem of a plant, forming a slit of variable width between two specialised cells (guard-cells), which allows movement of gases, including water vapour, to and from the intercellular spaces. Also, the whole pore with its associated guard-cells.