PAPR or Peak to Average Power Ratio is a way of characterising how far the waveform envelope peak exceeds the waveform mean.
It can be represented by a number or more usefully by a CCDF, showing the statistical probability of the envelope.
It is important in the correct specification of the linearity of a signal path through a system, especially for power amplifiers.
In the case shown above, whilst the mean signal power is 40dBm (10W), the peak power can be 48.3dBm (68W).
If a non-linear block in the signal path cannot handle 48.3dBm, then distortion occurs, such as poor EVM or ACPR.
Here is the case for a 2-carrier system:
Note that the mean power has increased by 3dB, or a doubling in power, ie 20W.
But the peak of the waveform has increased to almost 52.5dBm (176W).
The PAPR did not increase by 3dB due to the independent statistical nature of the two carriers.
This can be estimated using a Root-Sum-Square or RSS technique.