Question: what is the difference between concentrated sulfuric acid and fuming sulfuric acid?
Answer: If you look at them, you can see the difference. Sulfuric acid is not volatile, and looks like liquid. On exposure to typical laboratory air, fuming sulfuric acid gives off visible fumes (hence the name). This is because it contains SO3 (and generally some SO2) which is volatile, and some vapor comes off the surface.