And I don't mean the sort you make when walking in snow or on wet sand!
I must confess that in my first eleven or so years of camping I'd never heard of a footprint - it was only when I joined the forums of UKCampsite that I began to read about them and how they were recommended for anyone getting a new tent, and I finally realised that a footprint is a groundsheet which is an 'extra' to any particular model of tent and is the exact size and shape of said tent.
Like many people my first thought was 'why would you need one, is it so important?' but when, as a now-solo camper, I bought my small 4-berth tent which came with one as part of the deal I began to realise the advantages. Pegged down on a pitch before erecting the tent it shows just how much ground space the tent will use (ideal if you're trying to fit a large tent on a small pitch) and if you don't like it in one place it's easy enough to move it to another before putting the tent on top of it. It acts as a layer of insulation between the ground and you, and if you happen to be pitching your tent on a wet or muddy pitch it helps to keep the actual tent groundsheet clean and dry - when your camping break is over it's far easier to clean a footprint than it is to clean the groundsheet attached to a large tent.
So, from initially being fairly sceptical about these things I have, over the last three years, completely changed my mind about them, and the future purchase of any new tent will definitely include a footprint - and to anyone in any doubt, speaking from experience I can highly recommend them!
* Well there's no post tomorrow folks as Sunday is a day off from blogging, but I'll be back on Monday with G - if I can think of something to write!