Taking a look at the I-V graph

The graph typically has potential difference (V) on the x-axis and current (I) on the y-axis.
If the graph is a straight line passing through the origin, the component obeys Ohm's Law. If it's a curve, the opposite is true.
The gradient of the I-V graph at any point represents the reciprocal of the resistance (1/R) of the component at that particular voltage.
A steeper gradient means lower resistance, a shallower gradient means higher resistance.

I-V characteristic of an Ohmic conductor

When a metallic conductor is Ohmic, the I-V graph shows a straight line passing through the origin.
This means that resistance is constant and the conductor obeys Ohm's Law.
However, changes in temperature and pressure may cause the resistance to change, changing the gradient of the I-V graph.

The I-V characteristic of an NTC thermistor is a straight line (Ohmic) when the temperature remains constant.
However, the resistance decreases as the temperature increases, causing the gradient of the I-V graph to increase.
Many thermometers use the resistance of an NTC thermistor to determine the temperature of the environment.