What is Subsidiary Communications Authorization or SCA in FM Broadcasting?

"A subcarrier, known also as Subsidiary Communications Authority or SCA, is a separate audio or data channel which is transmitted along with the main audio signal over a broadcast station. These subcarrier channels are not receivable with a regular radio; special receivers are required. Subcarriers are used for many different purposes, including (but not limited to) paging, inventory distribution, bus dispatching, stock market reports, traffic control signal switching, point-to-point or multipoint messages, foreign language programming, radio reading services, radio broadcast data systems (RBDS), station control and meter reading, utility load management, and muzak. A broadcast station may transmit more than one subcarrier signal. Licensing of subcarrier operations ended in 1983 when the service was deregulated."