Physical layer - carrier wave
A carrier wave or carrier signal is a waveform that exists on any active telecommunication circuit. This waveform, which most often is in the form of a sinusoidal wave, as shown below, is a wave of alternating current sent over a copper wire.
This waveform exists on the wire or in the air even when no data is being exchanged. When data is exchanged, the waveform’s properties are modulated or modified in particular ways. The modifications in the waveform contain data that can be demodulated or interpreted on the other end of the link. The placement of information onto a waveform using modulation is called encoding. Such carrier waves are seen in technologies including Ethernet and Wi-Fi.
All of the above are elements of communication that exist on the physical layer of the OSI Model.