We use the term greenhouse gases to cover a number of gases identified as drivers of climate change by the United Nations Framework Convention on Climate Change (UNFCCC): carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, sulphur hexafluoride and nitrogen trifluoride.
To make things simple and comparable across businesses and other polluters, we translate the climate impact of all greenhouse gases into a single measure: carbon dioxide equivalent (CO2e). For example, a gas twice as potent as carbon dioxide (from a climate impact perspective) is assigned two tonnes of CO2e for every one tonne emitted.
When we discuss greenhouse gases, carbon or emissions then usually the CO2e is our best absolute measure.