Obsolescence - Loss in value due to obsolete or out-of-date design or construction.

Offer and Acceptance -  A contract used in the sale of real property; a deposit receipt or exchange agreement.

Offer to Buy - An agreement between owner and purchaser as to the price, terms, conditions and date of occupancy. Usually prepared by a Realtor or attorney.

Open End Mortgage - A mortgage agreement such that the mortgager can borrow additional funds in the future without rewriting the mortgage.

Open Listing - A listing agreement whereby either the owner or the broker can sell the property; if the broker is the procuring cause, a commission is due.

Option - A contractual right given for a consideration permitting a person to lease or buy the property at a specified price within a given period.

Optionee - A person who holds an option.

Optionor - A person who gives an option to another person.

Oral Contract - A verbal agreement; one which is not reduced to writing.

Ordinance - A law passed by the legislative body by a municipal corporation.

Overhang - The portion of a roof extending beyond the walls.