1. You are about ready to purchase a parcel of real estate. Before closing the sale, you have a title insurance company do a preliminary title search to make sure there are no defects in your title. Everything is OK, so you arrange to close the sale as soon as the title insurance company can issue you a policy. The title insurance company does a last-minute search to make sure there haven't been any changes, closes the sale, and issues you a title insurance policy.
2. The title insurance company finds that the seller's title is fine, but alas - you are paying for the property with a bank loan, and the bank wants a mortgage on the property in exchange.
So tell the closing agent to get you a title policy that makes an exception in its coverage for your mortgage. The bank, meanwhile, will issue the money only when it receives a title policy showing that it has a valid first mortgage on your property. Except for that mortgage, you're covered against any encumbrances or other title defects on the property.
3. Your title insurance company checks out the seller's title and discovers that it has a mortgage on it (probably taken out when the seller purchased the property). So make sure that the closing agent closes escrow only when the title insurance company issues a policy that does not list the owner's mortgage as an exception to its coverage. Of course they're not gonna do that until the mortgage is paid off, thus putting the ball in the owner's court. But you can smooth this one over by agreeing with the owner that part of your purchase money be paid to the holder of the mortgage in order to extinguish it. This will clear up the title and cause the title insurance company to issue a policy with no exceptions, clearing the way for you to close the sale on your terms.