A carrier frequency is a single radio frequency with steady amplitude.
Alone, it would sound like silence on a receiver.
This is the frequency that a radio receiver is tuned into.
To be of use in communication, this carrier wave has to be changed in time with another signal (usually audio), called ‘Modulation’
It can be turned on and off using a Morse key.
It can be changed by shifting the frequency, FM.
It can be changed by varying the amplitude, AM.
It can be changed by adding or subtracting audio to the carrier. Single Side Band.
It can have data applied by shifting between two carrier frequencies. FSK. (Frequency shift keying.)
It’s called a carrier, because it is the carrier of information without necessarily being the information itself.