The Clipper Card is a smart card used for public transportation in the San Francisco Bay Area. It allows users to pay for rides on various transit systems, including BART, Muni, Caltrain, and AC Transit. The card can be loaded with cash value or transit passes, making it convenient for daily commuters and visitors alike. Users can easily tap their Clipper Card on card readers when boarding or exiting transit vehicles. The card can be reloaded online, at ticket machines, or at retail locations, providing flexibility and ease of use for anyone traveling in the San Francisco region.