Also an uncommon (at least among the people I know) cycling term, referring to pain or numbness in one or both feet - caused by the use of clipless pedals.
It usually occurs due to using 'incorrect' (too much or too little) float. The point at which pain occurs varies with the individual, but mainly it's at the extremes - 10+ degrees of float, such as with Speedplay pedals, or no float at all. Float is not the only cause, but for any cyclist that has been using clipless pedals for long enough to have correctly aligned cleats, it is the most common.
The pain is caused by compression of the nerves between the metatarsals, and is often a precursor to serious knee pain as the foot stretches uncomfortably and holds the ankle at a constant 'twist'.
If you experience hot foot, try first re-adjust your cleats so that they sit more comfortably. If the cleats are adjusted correctly (as is usually the case by the stage the symptoms become apparent) try first replacing your cleats before experimenting with other amounts of float. Older cleats, as they age, tend to wear in such a way as to provide uneven tension throughout the float, causing the muscles of your foot to strain at an odd angle.