What is aperture
The aperture refers to the size of the iris (hole) within the lens. The bigger the hole, the more light gets into the camera. Aperture is measured in F-stops. A low number like F1.8 or F2.1 means a wider aperture. F16 would be a smaller aperture. A wider aperture (a low F-stop) means less of the image is in focus. It also means a faster shutter speed can be used.