Carbon sequestration is the long-term storage of carbon dioxide (CO2) so it stays out of the atmosphere, where it would add to climate warming. According to the U.S. Department of Energy, the CO2 may be captured from power plants and industrial facilities or removed directly from the air, and scientists group storage methods into two broad types: biologic and geologic.
Biologic sequestration relies on the natural carbon cycle: plants take up CO2 through photosynthesis and move some of it into soils, while oceans hold it as dissolved gas and carbonate sediments. Geologic sequestration, also called carbon storage, compresses CO2 until it behaves like a liquid and injects it into porous rock formations deep underground, where it is trapped in pore spaces, dissolves in the fluids there, and eventually reacts to form stable minerals.
Source: U.S. Department of Energy, DOE Explains: Carbon Sequestration.
Image: Red Trail Energy ethanol CO2 capture plant in Richardton, North Dakota, by Acroterion (CC BY-SA 4.0), via Wikimedia Commons.