True fetish is when a person is sexually aroused by a specific object or objects and is generally unable to achieve sexual satisfaction without that object being present.
The key word there being object, as in inanimate. So foot fetish, isn't really a fetish under the strict definition. However, body part fetishists tend to objectify the feet, arm pits, ear lobes, whatever it is that flips their switch. For the sake of this biz the distinction is pretty much irrelevant. Whether their thing is feet or heels the behavior of the target audience is the same, and therefore so is the marketing.
My focus is more on fetish wear, just something special about dressing for sex.
The categories that I include on my sites: high heel shoes and boots, stockings, pantyhose, sexy lingerie (corsets, garters, bustiers, etc.), latex & pvc, leather, gloves, uniforms & costumes...
Besides assorted body part fetishes, other fairly common fetishes are behavior based. Smoking, wet & messy (mud, water, food, etc. usually while fully clothed or wearing some of the afore noted fetish attire), all the variations of BDSM, plus more that I'm probably forgetting.