Rent control is when the government steps in and caps the amount that rent can be raised annually, usually applicable to occupied units. When the units are vacant, usually the owner can raise rent as much as the market will bear, which they will.
Low income is housing designated for people who make a low wage, the caps designated by the government. Maybe 80% of median income. 
Affordable housing is something that someone is magically going to produce. St Vinny's offers affordable housing to low income people and will be subject to rent control should that come in to effect.
Rent control is a bad idea. Horrible. It won't help low-income people. Owners will top out rents at every opportunity, raise rent to the maximum allowed annually, and will cut no slack to any renter. Those who have blemished rental history will be SOL. Deposits will increase. Not good, not good, not good.

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