A Multiple Listing Service (MLS) 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.
MLS databases are used by brokers to share information about properties to help find a buyer for the property.