A foot pod (aka running pod) is a small device that measures distance by sensing the motion of your foot. It works by detecting the acceleration / deceleration of your foot each time you take a step, so it can adjust to changes in your stride as you run at different speeds over varying terrain.
Once calibrated, foot pods can provide distance measurements with accuracy similar to GPS devices. In locations where GPS reception is poor, they may even provide better distance data.
Like most GPS devices, some foot pods can also show your current pace; but most lack the ability to save data for later analysis. Mapping our course is not possible because foot pods do not gather location data.
Nike, Polar, Suunto, and FitSense all have foot pod type devices.