A pedometer is a device that counts the number of steps walked, and also estimates distance covered (based on stride length) and calories burned in the process (based on body weight). I acquired one recently to find out how much walking I do in my daily life. It's an Omron HJ-112, and I have no idea how it works, except I keep imagining that it contains artificial semicircular canals. That's probably not it, but it manages to be pretty accurate as long as I either clip it to some part of my clothing that doesn't move much (the top of my pants works well) or keep it in a snug pocket. Too much swinging around in a loose pocket confuses it mightily, as does walking funny.
The recommended walk count is 10,000 steps per day. I get nowhere close to that. On a workday it tends to be somewhere between 2000 and 2500, and on weekends it's much less - but that's partly because I forget to wear it while I'm bumbling around at home. Could I actually manage 10k steps in a single day? Hmm. I'd probably have to leave the computer and go outside. o.O