In one line: The deposit that makes an offer credible, held in escrow and governed by the contingencies.
Earnest money is the deposit a buyer puts up when an offer is accepted, typically around 1-3% of the price, held by a neutral escrow company rather than the seller. It is what the buyer stands to lose by walking away without a contractual reason.
The contingencies are what make it refundable: back out within your inspection, financing, or appraisal windows and the deposit comes home. Miss those windows and it can become the seller's consolation prize, which is why waiving contingencies to look strong has a price.
A worked example
On a $450,000 offer, a $4,500 deposit (1%) is typical in Las Vegas; $9,000 makes the offer stronger. It sits with the escrow company, comes back if a contingency fails in time, and is credited at closing if the deal goes through.
Questions people ask
How much earnest money is normal in Las Vegas?
About 1% of the price is the everyday figure, more in a competitive bid, and cash buyers on distressed homes are sometimes asked for more. It is negotiable; the contract, not custom, sets it.
When do I lose it?
When you back out for a reason the contract does not protect, or after a contingency deadline has passed. Walking away inside the inspection window with proper notice returns it; walking away the day before closing because you changed your mind does not.