Aperture - definition
The Aperture of a lens indicates how much light the lens lets in. The larger the aperture, the more light is let in, conversely a smaller aperture lets in less light. Measured in f-stops, these are inverse values, as shown in the aperture chart below, the larger the aperture the lower the f-stop number. An aperture of f/1.4 lets in more light than an aperture of f/8.