Section 8 is part of HUD – basically, low-income tenants get a subsidy from the government to cover their housing. When you advertise a rental as “section 8 OK” it means you are willing to do the paperwork necessary to get this thing rolling.
Lots of people will not take Section 8 tenants because of the low-income stigma, also because when the government gets involved, you know what happens. However, I have heard it is better to have a Section 8 tenant because you know you will get paid. Eventually.