Carbon Footprint refers to the the total greenhouse gas emissions that result from a person, organization, product or service over a given time.
It tends to act as an umbrella term for any attempt to measure greenhouse gas emissions and as a result can refer to simply the emissions that result from a single activity, such as flying; the emissions that result from an organization or building over the course of a year; or the full lifetime emissions of a product or organization, including emissions from the supply chain or disposal of resources.
While carbon footprints colloquially refer to the amount of CO2 emitted, the UK Carbon Trust endorses a wider definition and considers all six of the Kyoto Protocol greenhouse gases - Carbon dioxide, Methane, Nitrous oxide, Hydro fluorocarbons, Perfluorocarbons, and Sulfur hexafluoride - when measuring a carbon footprint.