Rent ControlledHardly any in the city, although your friend probably has one… The tenant has to have lived in the apartment for the last 30 years or handed it down from family member to family member. The rents are way below market value.
Rent StabilizedMore common than rent controlled apartments. They are under $2,000 a month and are regulated by laws that govern the amount the rent can be increased each year, normally between 2% and 5%, among other things. If they are renovated by the landlord or go over the $2,000 amount they become market rate. Some new full service buildings are rent stabilized although they have rents above the $2,000 range; they were given this status as a tax break by the city.
Market RateThe landlord sets the rent according to the market. They can raise the rent however much they choose to when the lease comes up for renewal but tend to follow the stabilized rent increases. This is the majority of apartments you will get in NYC.