A graduate certificate or diploma (the terms are used interchangeably in North America) in music denotes specialization in a sub-field or discipline of music gained through intensive graduate-level study. As such, it supplements an already established area of expertise (in music or not related to the field) and adds value to a previously earned Bachelor's or graduate degree. Delivered in various formats from residential to online, graduate certificates in music comprise 4 - 6 courses (typically 12 - 18 credit hours) taken in a prescribed sequence at the graduate level.
The concurrent graduate certificate or diploma in music allows students currently enrolled in a Master's or Doctoral degree program in the field to pursue an in-depth exploration of one aspect of their field. For example, a student working towards a Master's in Music with a specialization in Music Performance may take the Graduate Certificate in Sacred Church Music to augment their expertise.
The stand-alone, direct-entry graduate certificate/diploma program in music provides an opportunity for graduate-level study of theory and research to students who are not interested in pursuing a full graduate degree. This could include professionals with a Bachelor's degree working in the field or anyone who does not have the time or interest in a traditional graduate program in music. Then too, some students who take the stand-alone certificate already have a graduate degree and use their certificate to augment a particular area of interest.
A selection, but not inclusive list, of graduate certificates/diplomas in music includes

Graduate Certificate in Applied Music

Graduate Certificate in Music Studies (General)

Graduate Certificate in Music Composition

Graduate Certificate in Music Industry Management

Graduate Certificate in Music Technology

Graduate Certificate in Operatic Performance

Graduate Certificate in Music Performance

Graduate Certificate - Classical Music

Graduate Certificate - Jazz

Graduate Certificate in Sacred (Church) Music

Graduate Certificate in Scoring for Motion Pictures and Television