|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.