Voltage of pin set to high impedance?
If you set a microcontroller or FPGA IO pin to high impedance, the voltage there will be determined by whatever other components you hook that pin.

If you provide a pull-down resistor, the voltage will go low. If you provide a pull-up resistor, the voltage will go high. (It might also be possible to program the chip itself to provide a pull-up or pull-down resistor)

If you don't connect anything that can set the voltage, then it could even float randomly up and down, respond to capacitive coupling from nearby objects (like your body), etc.