ISO ( ) is a number that represents how sensitive your camera sensor is to light therefore effecting how bright or dim your photos will be.

A high ISO is suited to be taken in low light situations since the sensitivity is so low meaning you need a less amount of light to take a picture.

A low ISO is the opposite, and should be used in situations where the lighting is better since a low ISO means less sensitivity to light. Using low ISO in these conditions will reduce the amount of background noise in the photo leading to a high quality photo.

This photo was taken with a low ISO in dim lighting. This caused the image to become lower quality making it more grainy and resulted in more noise in the photo.