Aperture

[Sarah]

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

[Sarah]

1. A small narrow opening.

2. A fixed or adjustable opening in a piece of equipment such as a camera or microscope that lets light pass through a lens or mirror.

3. The diameter of an aperture in a piece of equipment such as a camera.

[Sarah]

A lovely little scientific research and development company enlisted by the American MoD to produce shower curtains, among other intra-dimensional projects. Responsible for the production of the Genetic Lifeform and Disk Operating System (GLaDOS), the Aperture Science Handheld Portal Device (Portal gun, if you prefer), and many, many innovative iterations of the world-famous shower curtain, Aperture are secretive in their operations and productive in their exploits. Future projects include life-enhancing gel, spherical personality buddies and tractor beams (or excursion funnels).

[Sarah]

A female photographer's vagina.

[Sarah]

A gaping orifice of uncomprehensible dimensions.

[Kai]

An opening, hole, or gap.