As the term implies, a foot fetish refers to someone who has a fetish that focuses on human feet. We don't know much about how common foot fetish is in the general population, but a study in 2007 which looked at Internet fetish communities and tried to estimate the relative popularity of one fetish over another reported that 33% of people who belonged to a fetish group had a fetish focusing on a part of the body, and of those, foot fetish was the most popular.
People with a foot fetish might get aroused by thinking of or looking at feet, or they might want to include the use of their feet, or more often a partner's foot or feet, directly in sex play. There is an amazing range among foot fetishists in terms of what they find arousing. It can be a certain type or shape of foot or a particular part of the foot (arch, toes, heel, etc…). Someone might have a particular smell that turns them on, or a specific kind of touch (e.g. being tickled or tickling feet, being stepped on, being kicked). There are also preferences for bare feet, feet in socks or stockings, or feet in shoes. People with foot fetishes may have a preference of the gender of the person whose feet are the focus of desire. Sometimes this matches the individuals identified orientation, and sometimes it doesn't.
While most people with a foot fetish are not public in their daily lives about it, there are a significant number of social groups, online forums, and products available for sale to people with foot fetishes. There is a seemingly endless amount of foot fetish pornography, and sex toy companies have for many years made sex toys in the shape of feet.
Scorolli, C., Ghirlanda, S., Enquist, M., et. al. "Relative Prevalence of Different Fetishes" International Journal of Impotence Research Vol. 19, (2007): 432-437.