Stain remover is designed to get rid of stains or marks that were left on a certain surface like a fabric. These are generally made from a solvent or detergent so that stains can be efficiently removed.
The rule of thumb, when it comes to stain removal, is that "like dissolves like." Butter, for example, is an organic fatty substance that is removed with an organic solvent. If you were to stain your shirt with hydrocarbon, bicycle grease, an organic solvent would not work. You would need a hydrocarbon solvent like gasoline to remove it.