Input Voltage Range
VIN Input Voltage Range The range of acceptable voltages applied to EITHER of the input pins
VD Difference Voltage Range The range of maximum voltage difference between the two inputs
VCM Common Mode Voltage Range The range of acceptable common voltages applied to BOTH inputs simultaneously

The inputs of the op-amp must stay within a certain voltage range for proper operation. Each of the two input pins of the op-amp has voltage swing restrictions, beyond which the op-amp will not work correctly or will behave non-linearly. Non-linearity means that aside from a change in the signal's amplitude, the information contained in the signal is changed and new information is introduced.

Below is an example from the MCP602 datasheet.

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