From the Department of Natural Resources web site:

The Maryland Park Service offers four different kinds of park passes. Select the pass that best meets your needs and link to the appropriate application that can be downloaded and mailed to the Maryland Park Service for your convenience.

• All Season Pass—Entitles free day-use entry, for everyone in the vehicle (up to 9 people), to Maryland’s state forests and parks; free boat launching; and a 10 percent discount on state-operated concessions and boat rentals. The 2007 Pass is now available online.
• Youth Group Pass—Entitles youth groups free day use admittance to Maryland State Parks and free camping in those parks that have designated “Youth Group” areas subject to site availability. This pass is not valid for day use entry on weekends and holidays from Memorial Day through Labor Day.
• Golden Age Pass—Entitles adults, ages 62 and older, free entry (cardholders only) to all State Parks that charge service fees. The pass is also valid for half price camping Sunday through Thursday.
• Access Maryland Pass—Entitles free lifetime entry to State Parks for individuals with disabilities.