A Format document sets out the type of broadcast output that each commercial radio station is required to deliver. It encapsulates the character of the service a station is obliged to deliver as a condition of its licence.
The holder of a national or local radio multiplex licence may apply to Ofcom to vary their licence as it relates to the digital sound programme services which are provided on the multiplex. This may be a request to change the Format description of an existing service (or services), a request to add or remove a service, or a request to change the technical parameters under which a service is broadcast (e.g. from stereo to mono).