It means that basically the property is free of liens and encumbrances such as mortgage, loans, debts or pending disputes. Make sure there is no individual or juridical entity that has any reason to have a hold on the property. If the property is mortgaged by the seller, ask for the latest statement from the lender and make an agreement with the seller whether it is paid by the seller prior to the closing of the sale (when you pay the price in full) or the assumed by the Buyer. Once the mortgage is paid in full, the lender should issue a certificate of Release of Mortgage to the current owner which should in turn be given to the Buyer. Ideally, the downpayment of the buyer should be enough to pay off the mortgage and the full payment is done when the release of mortgage has been issued by the lender.