Which measurement describes the lowest temperature at which oil will flow?

The pour point is the key measurement that indicates the lowest temperature at which oil can still flow. In practical terms, it defines the temperature limit for oil’s movement; below this point, the oil becomes too viscous and thickens, making it difficult or impossible to pump or utilize effectively in mechanical applications. This parameter is particularly important in applications where oil needs to start flowing after cold conditions, such as in engines and hydraulic systems.

The flash point, on the other hand, refers to the lowest temperature at which a liquid can form an ignitable mixture in air, which is critical for safety but does not directly relate to oil flow. The cloud point signifies the temperature at which waxes begin to crystallize in the oil, leading to the formation of cloudiness, which indicates potential issues in flow, but it's not the definitive measure for flowability itself. Lastly, the fire point is the temperature at which the oil can sustain combustion, and while it's also important for safety, it does not address the flow characteristics of the oil.