A micro is usually run out of of a private residence (house, condo or townhouse), generally operates without a business license and all the other financial burdens of a legitimate business, and brings in illegal aliens on tourist visas from Asian countries to service their clientele. The owners typically shy away from allowing Caucasians, as they are more likely to cause LE problems for them. They are often raided and closed down for the infractions listed above, but will frequently surface again in another neighbourhood. Their staff are put on a plane back to their place of origin, but the next flights from there will bring another batch.
That's about it.