Thanks for the answer. Do you mean 5V or 0.5? If you did mean 0.5V
The voltage on any pin should never be more than (Vcc + 0.5V)
...means the voltage on any pin should never be greater than half a volt more than the supply voltage (Vcc).
The voltage on any pin should never be less than -0.5V means not less than half a volt below
ground potential. This might occur with AC signals (which alternate above and below ground potential) or if dual-polarity supplies were involved.
is this why you see 10k resistors used with switches?
Hard to say what a 10K resistor might be for, without seeing a schematic. Strong possibility it is a pull-up or a pull-down resistor. OTOH, the m328 has built-in pullup resistors that can be used.