Generally it means Multiple Listing Service. It is a data base generally controlled by cooperating brokers who generally are Realtors. Only Realtors enjoy access to the MLS, real estate agents are not permitted access unless they agree to the local Realtor Board's rules and join. There is some contention on this issue related to potential anti-trust issues. This and other ethical considerations are why I refuse to be a Realtor.

A Multiple Listing Service is a suite of services that  enables brokers to establish contractual offers of compensation (among brokers);  facilitates cooperation with other broker participants;  accumulates and disseminates information to enable appraisals;  is a facility for the orderly correlation and dissemination of listing information to better serve broker's clients, customers and the public. A multiple listing service's database and software is used by real estate brokers in real estate (or aircraft broker[citation needed] in other industries for example), representing sellers under a listing contract to widely share information about properties with other brokers who may represent potential buyers or wish to cooperate with a seller's broker in finding a buyer for the property or asset. The listing data stored in a multiple listing service's database is the proprietary information of the broker who has obtained a listing agreement with a property's seller.

Generally it means Multiple Listing Service. It is a data base generally controlled by cooperating brokers who generally are Realtors. Only Realtors enjoy access to the MLS, real estate agents are not permitted access unless they agree to the local Realtor Board's rules and join. There is some contention on this issue related to potential anti-trust issues. This and other ethical considerations are why I refuse to be a Realtor.

Check out this old blog posts:

http://www.realty-tx.com/blog/real-estat…