What is a Carbon Footprint?

Carbon footprint - an individual's carbon footprint is the direct effect one's actions and lifestyle have on the environment in terms of carbon dioxide emissions. This is usually estimated by using a Carbon Calculator. From our home electricity use, to travel, to our diet, to the clothes we wear, all of our actions involve emission of carbon dioxide and have direct or indirect impact in accelerating climate change.
http://www.dcnr.state.pa.us/brc/grants/Glossary.doc
The pie chart above shows the main elements whichmake up the total of a typical person's carbon footprint in the developed world.

carbon footprint is made up of the sum of two parts, the primary footprint (shown by the green slices of the pie chart) and the secondary footprint (shown as the yellow slices).

1. The primary footprint is a measure of our direct emissions of CO2 from the burning of fossil fuels including domestic energy consumption and transportation (e.g. car and plane). We have direct control of these.

2. The secondary footprint is a measure of the indirect CO2 emissions from the whole lifecycle of products we use - those associated with their manufacture and eventual breakdown. To put it very simply – the more we buy the more emissions will be caused on our behalf.
http://www.carbonfootprint.com/carbonfootprint.html