Job Creators: We, the 99% of the population who are not the upper-class, are actually the job creators. We create jobs though the expenditure of our wages and labor. The 1% don't create jobs...they're largely the "economic vampire" class.
Middle Class: The middle class was for the majority of the 20th century the large class of the population that were neither the destitute-poor or the much-smaller class of the wealthy. At that time, the majority of America's wealth was in the hands of the middle-class; a class made up mostly of skilled-labor which rose in economic prominence following WW II. The vast majority of people posting on DU are middle-class or would have been if the GOP had not destroyed the economy and shoved us back into poverty.
Small Business: This one seems the easiest but is in some sense the trickiest. A small business is a business that has few enough employees that the owner actually knows who the people working for him are. It's a business where if you call up and ask to speak to the owner, you can usually get them on the phone. It's a business that often times but not always has a connection to a specific locale. In a more technical sense, it's a business with less than 500 employees and revenues under $5M/year. Most small businesses today are home-based sole-proprietorships--I am one; I am a freelance writer and I teach creative writing. Most small business owners are members of the middle class. None of these are really a great answer, they seem to dance around a definition rather than bulls-eye it.