Feet marks material in which feet are a point of focus rather than incidental. In a gay context this can range from bare feet and socks appearing prominently, to attention being paid to them as part of the action. It says something about where the emphasis falls, not about what else takes place. The term sits near vocabulary like bondage and BDSM, since foot-focused material sometimes overlaps with those interests, though it just as often stands on its own. Related words such as bareback describe condom use rather than a type of act, so they answer a different question than this tag does.