A spot is a substance that is adhered to the carpet fiber, but has not become set. A stain is more advanced and may have become set.
A professional carpet cleaner will remove all spots (food, grease, mud, etc).
A professional carpet cleaner will have more problems removing a set or permanent stain compared to a spot. We carry a large amount of stain removal solutions for the removal of coffee, tea, blood, cola, urine, red wine etc. If the stain has not set and become permanent, stain removal can be successful.