Exposure

The product of intensity and time interrelations of shutter speed and aperture setting.

Shutter Speed

A mechanical device that open and closes to regulate the period of time that light is allowed to pass throught the lens.

Shutter speed is measured in seconds - or in most cases fractions of seconds. The bigger the denominator the faster the speed (ie 1/1000 is much faster than 1/30).
In most cases you’ll probably be using shutter speeds of 1/60th of a second or faster. This is because anything slower than this is very difficult to use without getting camera shake. Camera shake is when your camera is moving while the shutter is open and results in blur in your photos.

What is Aperture?

The main function of a camera lens is to collect light. The aperture of a lens is the diameter of the lens opening and is usually controlled by an iris.The larger the diameter of the aperture, the more light reaches the film / image sensor. Aperture settings are called f-stops and indicate the size of the aperture opening. Each f-stop lets in half as much light as the next larger opening and twice as much light as the next smaller opening.

What Is ISO?

ISO is the number indicating a digital camera sensors sensitivity to light. The higher the sensitivity, the less light is needed to make an exposure. Digital cameras automatically select the ISO but most have a setting to change it manually.

Example Number of ISO:-
0, 12, 25, 32, 50, 64, 100, 125, 200, 400, 800, 1000, 1600, 3200, 6400, 12000, 25000

Note:- The higher the number, the more noise. The amount and degree of noise varies from camera to camera.

Standard;-
ISO - International Standard Association.
ASA - American Standard Association.
DIN - Deutsche Industrie Norme