A footprint is the mark your foot leaves behind when you step in mud, sand, or snow. You can see your own footprints trailing behind you on a beach, showing exactly where you walked. Detectives might find footprints at a crime scene that help identify a suspect. Animal trackers follow footprints through the forest to learn which creatures passed by and where they went.

The word has grown to mean the amount of space or impact something takes up. A building's footprint is the area of ground it covers when you look down from above. When people talk about their carbon footprint, they mean the total amount of carbon dioxide their activities release into the atmosphere, like driving cars, using electricity, and buying things that were manufactured and shipped. Someone with a large carbon footprint uses more resources and creates more pollution than someone with a small one.

You might also hear about a company's environmental footprint (all the ways it affects nature) or its digital footprint (all the information about it that exists online). In each case, footprint describes the mark or impact left behind, just like those tracks in the sand.