Amateur radio (also called ham radio) describes the use of radio frequency spectra for purposes of non-commercial exchange of messages, wireless experimentation, self-training, private recreation and emergency communication. The term "amateur" is used to specify "a duly authorised person interested in radioelectric practice with a purely personal aim and without pecuniary interest;" (either direct monetary or other similar reward) and to differentiate it from commercial broadcasting, public safety (such as police and fire), or professional two-way radio services (such as maritime, aviation, taxis, etc.).