Suppressed-carrier transmission is a special case in which the carrier level is reduced below that required for demodulation by a normal receiver.
Carrier power must be restored by the receiving station to permit demodulation, usually by means of a beat frequency oscillator (BFO).
Failure of the BFO to match the original carrier frequency when receiving such a signal will cause a heterodyne.
Suppressed carriers are often used for single sideband (SSB) transmissions, such as for amateur radio on shortwave.
That system is referred to in full as SSB suppressed carrier (SSBSC) or (SSB-SC).