A tarp is a heavy-duty strong flexible sheet that has grommets at four sides. It is mostly used to cover your tent from the sun, rain and even snow, on the other side footprint is a very lightweight friction-resistant sheet you put under your tent.
Tarps have a fabric that has similarities with a trampoline it is flexible and it is very strong. And so you can use it to cover your tent and some other goods and it can act as the sun, you can sit in the shade and enjoy your time.
Tarps also protect you from snow if you are camping in snowy season snow might pile on your tent it might be dangerous but if you have a tarp to cover it, it will take care of it.
Can you use a tarp as a tent footprint? yes you can, if you use a footprint as a tarp, it won’t give you the protection tarp would give you, but if you use a tarp like a tent footprint it would be great because it is thick and will give your tent enough protection.