I fly back and forth from the EU to the US and I've flown multiple times in business or first, and to this day I have no idea what the difference is between the

I fly back and forth from the EU to the US and I've flown multiple times in business or first, and to this day I have no idea what the difference is between the two. If they charge more for one than the other, then I'd really like to know what they're charging for.