Maximum Vin on load switch ICs
Vin will be measured with respect to some other pin. Usually, this pin will be the Ground pin, the 0v reference, for the power supplies and the logic control. The switch input must not be more than Vin(max) voltage difference from this pin. Too much voltage difference can over-stress the internal structures and break the IC. If there's a Vin(max) on the data sheet, it's there for a reason.

Often, a data sheet will quote several maximums, so maximum switch current, maximum voltage under this condition, maximum voltage under that condition, maximum power dissipation etc. All limits have to be respected, or you're likely to break the IC.