Seller concessions are amounts the seller agrees to contribute toward the buyer's side of the deal — most commonly covering part of the buyer's closing costs, prepaying items like insurance or taxes, or funding a temporary or permanent interest-rate buydown. They are negotiated into the purchase contract and show up as credits on the settlement statement. Lenders cap how much a seller can contribute, and the cap depends on the loan program and down payment, so the ceiling is a question for your lender.
Concessions are really a form of price: a $300,000 sale with $9,000 in concessions nets the seller about the same as a $291,000 clean sale, but the buyer needs less cash at the table. That makes them a favorite tool in slower markets and for cash-constrained buyers. The caution is that the appraisal still has to support the gross price — concessions baked into an inflated price can push a deal past what the property appraises for.