Closing costs are the fees you pay to actually get the loan and transfer the home — separate from, and on top of, your down payment. They typically run a few percent of the loan amount and bundle many charges: the lender's origination fee, appraisal and credit report fees, title insurance, recording charges, and prepaid items like homeowners insurance and property taxes to seed your escrow account.
You will see them itemized twice: first as estimates on the Loan Estimate shortly after you apply, then finalized on the Closing Disclosure before signing. Compare the two documents — a lender's own fees generally cannot jump much between them, and unexplained increases are worth pushing back on.
You can trim the bill by negotiating seller credits, shopping for the title work yourself, or rolling costs into the loan (which raises your balance and long-run interest). For a line-by-line tour of what each fee actually buys, see closing costs explained.