Bump in between toes
Welcome to BYC. A picture of the bottom and and of the foot would help. It may be bumblefoot which is usually a staphylococcal bacterial infection on the footpad that happens due to tiny cut. They will usually cause a red swollen footpad with a dark spot, and sometimes the infection will spread to the upper side of the foot between the toes. Here are some links to help you if you want to try soaking the foot in a warm bath with betadine or epsom salts, or if you want to try the surgery:
Bumblefoot infection in the bottom and top of foot
Edited by Eggcessive - 10/25/15 at 10:49am
Welcome to BYC - as Eggcessive posted above, the first thing that comes to mind with just the description is bumblefoot, but it would be most helpful if we could actually see the foot/bump in question as what we are picturing from a description may be different than what we would see.