If one volt of potential difference across a device causes on ampere of current to flow, then the device has a resistance of
Often the current through an object is proportional to the potential difference across it over a wide range of values.
The resistance is then a constant and the object is said to obey Ohm's Law.
Ohm's Law is not exact. Even a metal wire shows variable resistance when enough current flows through it to heat it up.
Many useful devices show extreme departures from Ohm's Law.
Most of your electrical resistance is in your skin and varies from 500 ohms (clean) to several million ohms (dirty).