An origination fee is what the lender charges for making your loan — processing the application, underwriting it, and getting it to the closing table. It's often quoted as a percentage of the loan amount, sometimes as a flat fee, and it's part of your overall closing costs.
Here's why it deserves your attention: unlike appraisal or title charges, the origination fee goes straight to the lender, which means it's one of the few closing costs that's genuinely negotiable and varies widely between lenders. You'll find it in Section A ("Origination Charges") of your Loan Estimate — and by rule, Section A fees can't increase between the estimate and closing except in narrow circumstances.
One trap to avoid: a lender advertising "no origination fee" isn't running a charity. The cost usually reappears as a slightly higher interest rate. That trade can actually be smart if you'll sell or refinance soon, and backwards if you're staying put for decades — it's the mirror image of paying discount points to buy the rate down. Compare offers on the combination of rate plus Section A fees, never on either number alone.