Advance payment refers to the payment of a certain amount of money to the other party according to the agreement as a guarantee of claims. After the debtor fulfills its debts, the deposit shall be offset against the price or recovered. If the party paying the deposit fails to perform the agreed obligation, it shall not have the right to request the return of the deposit; If the party receiving the deposit fails to perform the agreed debt, it shall double the deposit.
According to the above definition, Xiao Li paying 20,000 yuan to the landlord after fancying a second-hand house and the two sides agreeing to sell the house to Xiao Li within a week is advance payment.