Greenhouse Gases (GHGs) – Gases that trap heat in the atmosphere, absorbing the sun's energy and emitting thermal radiation, causing the earth to warm at a faster rate than usual. Principle GHGs are carbon dioxide (CO2), Methane, Nitrous Oxide, and fluorinated gases.

Emissions – Gases and particles which are put into the air by various sources, including point and mobile sources.

Avoided Emissions – Emissions that would have been emitted under a business as usual scenario but were avoided due to the implementation of an emission reduction project.

Carbon Sequestration – The process of removing carbon from the atmosphere and depositing it in a reservoir. This is often the process by which atmospheric carbon dioxide is taken up by plants, soils and water. Trees, grasses, and other plants photosynthesize and store carbon in biomass (trunks, branches, foliage, and roots).

Project implementers should calculate GHG emissions avoided or sequestered as a standard part of project planning for applicable projects, such as compact development and alternative transportation. Implementing agency project managers should report any pre-project analyses as expected accomplishments, and modify during project implementation.