A Multiple Listing Service (MLS) is a private, cooperative database created and maintained by real estate professionals to share information about properties for sale. It serves as a comprehensive repository that tracks the full lifecycle of a listing, including its status as active, under contract (pending), sold, expired, or withdrawn. This detailed historical and current data is the primary tool used by licensees to conduct comparative market analyses (CMAs), advise clients on pricing, and facilitate cooperation and compensation between brokers.

A. This describes a print media advertising model (e.g., a newspaper), which is fundamentally different from the digital, data-driven structure of an MLS.

B. The MLS is not a free service; it is a subscription-based tool for which member real estate professionals pay dues and fees to access and use.

D. While the MLS is a proprietary system for real estate professionals, this answer is incomplete. Its core identity is its function as a comprehensive database, not just its access restrictions.

1. National Association of REALTORS®. (2023). Handbook on Multiple Listing Policy. Section 1, Definition of Multiple Listing Service. The handbook defines an MLS as "a means of accumulating and disseminating information to enable authorized participants to prepare appraisals, analyses, and other valuations of real property for bona fide clients and customers." This confirms its role as a comprehensive information database.

2. Galaty, F. W., Allaway, W. J., & Kyle, R. C. (2022). Modern Real Estate Practice (21st ed.). DF Institute, Inc. Chapter 5, "Real Estate Brokerage," explains that an MLS is a marketing organization whose members make their listings available for showing and sale by other members, maintaining a database of listings that includes past and present data.

3. Maryland Real Estate Commission. (2022). Maryland Real Estate Practice & Law (16th ed.). Chapter 10, "Pricing the Property." This text details how licensees rely on the MLS database, which contains "properties that have recently sold, are currently on the market, and those that did not sell (expired listings)," to prepare a Comparative Market Analysis (CMA). This highlights the MLS's function as a database of various listing statuses.