Maximum level
When the input attains a certain level, the system will no longer have a linear response due to the physical limits of the system (electronic or mechanical saturation). The output will stay at its maximum (the supply voltage for an amplifier for example), until the input is decreased. If the input is not reduced, then the device can be damaged or destroyed. It is not uncommon to see speakers with the tweeters burnt out due to very high levels.
Hence, it is mandatory to indicate the maximum admissible input levels for a specified quantity (distortion, heat dissipation, etc).
