In DC law there is no such thing as a "concession." 

There are 34 definitions in the part of the law governing rental housing. There are definitions of "housing provider," "rental unit," "housing regulations," "person," "mayor" and 29 other terms -- but no mention of "concessions." Nor does the word appear in any other part of the rental housing statute.

When a housing provider use the word "concession" it means a "discount." However, that isn't what it is at all.

Webster's dictionary defines the word "discount" as "a reduction made from a regular or list price." Most people know exactly what a discount is. If a car normally sells for $20,000 and lots of people have bought that model for $20,000, when a car dealer advertises the same car for $15,000 it is a $5,000 discount. A discount makes the selling price lower than the usual market price.

Some housing providers advertise their apartments at a competitive market price -- let's say $1,500 per month for a one-bedroom apartment. But when a prospective tenant sits down to sign a lease, at the very last minute the leasing agent reveals that the "rent" is really e.g. $3,500 per month. But with a $1,500 "concession," supposedly a discount, the housing provider will let you have the apartment for only $1,500, the competitive market price that was advertised.

So the "concession," supposedly a discount, is added, not subtracted, from the market price, creating a "rent" that is impossibly high, e.g. $3,500. The leasing agent misleads you into signing a lease listing the rent as $3,500, with a $1,500 "concession," supposedly a discount. But this is no bargain because next year you'll really, really regret that you did that.