What is the meaning of footprint?

noun

• A mark of a foot or shoe on a surface.
  • usage: "the police made casts of the footprints in the soft earth outside the window"
  • synonyms: footmark, step
• A trace suggesting that something was once present or felt or otherwise important.
  • usage: "the footprints of an earlier civilization"
• The area taken up by some object.
  • usage: "the computer had a desktop footprint of 10 by 16 inches"