There are no liquids that do not freeze. However, under certain conditions, it is possible to cool a liquid below its normal freezing point. Such a substance is called a supercooled liquid.
The temperature at which a liquid freezes under atmospheric pressure is called the normal freezing point. In order for a liquid to have the property of never freezing, its freezing point must be absolute zero, the lowest temperature that matter can reach: 0 Kelvin or -459.67 degrees Fahrenheit. Currently, no such liquid has been discovered; thus, every liquid freezes if cooled to a sufficiently low temperature.
It is possible for a liquid to remain a liquid at temperatures below its normal freezing point. To achieve supercooling, the liquid must be prevented from nucleating, or forming very small frozen crystals. This can be done by isolating the liquid from movement and storing it in a completely clean and smooth vessel. For some liquids, lowering the surrounding pressure while cooling can also lead to supercooling. However, supercooled liquids are highly unstable, and they freeze completely once nucleation begins. A small imperfection in the vessel or a tiny disturbance, such as tapping the vessel, causes the supercooled liquid to nucleate and solidify.