Cooking fats vary if they are solid or liquid at room temperature. When making mayonnaise or salad dressing, oil must be completely liquid at refrigerator temperature.
Salad dressing manufacturers test the cloud point. This is the time it takes for cloudiness to appear when immersed in an ice bath. A time of 5.5 hours is considered minimum. A time of 20 hours is very good. In manufacturing, a rapid test is done by chilling the oil sample to –76°F for 15 minutes, then at 50°F. If no solid matter remains after 30 minutes, the oil passes the test.
The smoke point is the temperature at which heating oil starts to give off smoke.
Source: Fats & Oils: Practical Guides for the Food Industry, Eagan Press Handbook Series