OBSOLESCENCE - A type of depreciation of property.

OFFER - A promise by one party to act or perform in a specified manner provided the other party will act or perform in the manner requested.

OFFER AND ACCEPTANCE - The two components of a valid contract; a "meeting of the minds."

OFFICE EXCLUSIVE - A listing in which the seller refuses to submit the listing to Multiple Listing Service, even after being informed of the advantages of MLS, and signs a certification to that effect.

OFFSITE COSTS - Costs such as for sewers, streets, utilities, etc., which are incurred in the development of raw land, but are not connected with the actual construction of the buildings(onsite costs).

OPEN-END MORTGAGE - A mortgage in which the borrower is given a limit up to which he may borrow, with any incremental advances of money up to but not exceeding the original borrowing limit to be secured by the same mortgage.

OPEN HOUSE - The common real estate practice of showing a listed home to the public during established hours, frequently on Sunday afternoons.

OPEN LISTING - A listing given to any number of brokers. The first broker who secures a buyer ready, willing and able to purchase at the terms of the listing is the one who earns the commission.

OPEN SPACE - Certain portion of the landscape which has not been built upon and which is sought either to be reserved in its natural state or used for agricultural or recreational purposes(such as parks, squares, and the like).

OPERATING EXPENSES - Those periodic and necessary expenses which are essential to the continuous operation and maintenance of a property.

OPINION OF TITLE - An opinion by a person competent in examining titles, usually a title attorney, as to the status of the title of a property.

OPTION - An agreement to keep open, over a set period, an offer to sell or purchase property.

ORIGINATION FEE - The finance fee charged by a lender for placing a mortgage, which covers initial costs such as preparation of documents and credit, inspection and appraisal fees.

OVERIMPROVEMENT - An improvement which by reason of excess size or cost is not the highest and best use for the site on which it is placed.

OVERRIDE - A commission paid to managerial personnel (e.g. principal broker) on sales made by their subordinates, usually calculated as a percentage of the gross sales commissions earned by the salesperson.