A footprint is the mark left by your feet on the ground or floor. If you dog runs away from you on the beach, you might find her by following her footprints in the sand.
Your dad might scold you for tracking footprints across the clean kitchen floor — or you might hurry outside after a blizzard to be the first person in your neighborhood to make footprints in the fresh snow. A footprint is proof that you were there: similarly, a figurative kind of footprint is evidence of someone or something's presence or influence. For example, a company's "carbon footprint" is the amount of polluting greenhouse gas it emits.