Aperture

Credit goes to Shinka for providing this photograph 

Credit to- unknown 

1. We can closely relate aperture to the pupil.

2. Finish this sentence - The smaller the Aperture the smaller amount of light, the higher the Aperture the higher amount of light.

3. The larger a f-number (which provides smaller aperture) will bring the foreground and background images in focus, while a smaller number will isolate the foreground from the background, and making foreground images more focused and background blurry.