The act of opening.

An opening; an open space; a gap, cleft, or chasm; a passage perforated; a hole; as, an aperture in a wall.

The diameter of the exposed part of the object glass of a telescope or other optical instrument; as, a telescope of four-inch aperture.

The major opening of a gastropod shell.

The effective cross-sectional area of the antenna. The larger the aperture, the stronger the signal the antenna receives or transmits.

In a directional antenna, the portion of a plane surface very near the antenna normal to the direction of maximum radiant intensity, through which the major part of the radiation passes. In an acoustic device that launches a sound wave, the passageway, determined by the size of a hole in the inelastic material and the wavelength.

The cross sectional area of an antenna. Also called "Capture Area".

30 the curved slot through which the oculus is exposed.

Modification of the exine of a pollen grain or spore that is the site of exit for the contents (e.g., laesura, colpus, pore).

(adj. aperturate) (( Erdtman, 1947) A specialized region of the ( sporoderm, that is thinner than the remainder of the sporoderm and generally differs in ornamentation and/or in structure. Comment: Apertures are described as simple if they are present in only one wall layer, or compound if they affect more than one layer of the wall. In compound apertures the shape of apertures may differ between layers. Ectoapertures occur in the sexine/ ectexine, endoapertures in the nexine/ endexine, and mesoapertures are sometimes found in an intermediate position between an ecto- and endoaperture. Various types of apertures are recognised on the basis of their shape (see, colpus, laesura, porus, sulcus, ulcus), position (see, ana-, cata-, zona-, zono-) or fusion (see, syn-). In living pollen grains or spores the apertures usually function as sites of germination, they may also provide routes for transfer of water and other substances, and play a part in harmomegathy. The term is often used in conjunction with a prefix or suffix, as for example in, ectoaperture, endoaperture, inaperturate, omniaperturate, pseudoaperture, triaperturate.

Apertures are very small spots on the walls of a pollen, where the wall is thinner and/or softer. For germination it is necessary that the pollen tube can reach out from the inner of the pollen and transport the chromosomes to the egg deep down in the pistil. The apertures are the places where the pollen tube is able to brake through the elsewhere very tough pollen wall.

Window that displays the date within the dial of the watch

Where the date is displayed within the dial of the watch

The dials of some watches have apertures in which certain indications or the watche's movement are shown (e.g. the date, the hour)