A “carbon footprint” is a measure of how much impact a person or group is contributing to global carbon dioxide emissions. Carbon dioxide levels in the atmosphere have been increasing and many are concerned that higher carbon dioxide levels will contribute to a “greenhouse effect”, changing global climate patterns.
Basically, your carbon footprint is the total amount of carbon dioxide and methane emissions you produce from your daily activities, such as driving, mowing the lawn, and washing your clothes. Minimizing the amount of fuel and energy you use reduces the amount of harmful gasses you emit into the atmosphere.
There are many calculators available to help you calculate the effect you have on the environment. Here are a few:
Here are a few great visuals that help explain “carbon footprint”: http://www.carbonvisuals.com/