Neatsfoot oil is a special kind of oil that comes from the feet and legs of cows. It's called "neatsfoot" because in the old days, people used to think it came from the nose (or "neat") of the cow, but really it comes from the legs.
People use neatsfoot oil to take care of leather things like shoes, boots, and belts. When leather gets dry or stiff, neatsfoot oil can make it soft and shiny again. It's kind of like putting lotion on your skin when it gets dry.
The oil is made by taking the fat out of the cow feet and legs and heating it up until it turns into a liquid. Then it's cleaned and packed into bottles. Sometimes people mix neatsfoot oil with other things like beeswax to make it work even better on leather.
So, in summary, neatsfoot oil is a special oil made from cow feet that can soften and shine leather things.