Over-The-Counter Market
  
See: Over-The-Counter - OTC.
It's a simple market. It trades about like cantaloupe, pounds of burger, and tubes of toothpaste at the corner market. The OTC market is kind of the non-prescription medicine of trading markets. And those who live there sorta trade by appointment. Not a lot happens, relative to a major market like NASDAQ or the NYSE. There aren't a ton of regulations either. Crappy, er, um...small companies can be listed on the OTC for trading in their shares, often with a fraction of the paperwork of a major exchange. See: Shelf Registration. See: Regulation A.
If you haven't seen Wolf of Wall Street, well, a) you should, and b) they traded a ton on the OTC, taking massive commissions for the privilege. Caveat Emptor.