Listing inventories is a term used by real estate agents to describe the number of housing units that are available for sale in a given geographic area; such units include all single-family homes as well as all condominiums, townhomes and co-ops. In other words, when someone is interested in purchasing a home, the agent he or she is working with consults the listing inventory to find properties that fit what the buyer is looking for. In addition, when news stories mention that the listing inventory is up or down nationwide or in a certain area, they are referring to the number of housing units that owners have put up for sale. The listing inventory is further broken down by age or the number of days it has been for sale and by the median price of all homes for sale at that time. The listing inventory changes as homes are sold and new ones are added.