When you put food in oil it's at s much hight temperature than boiling in water. As a result moisture in the food is boiled out which dies the food. Its also hot enough that browning (maillard reactions) and crisping can occur.

The bubbling when you deep fry is the water coming out of the food and vaporising. You can get pills to boil as well, although they aren't pure liquids boiling is generally accompanied by a lot of smoking, burning of components in the oil, and - because oils are generally flammable - the vaporised fraction often ignites.

To boil is to heat a liquid to point of vaporization. Like water to 100 °C. Oils boil much higher, like 300-400 °C.

Fry is a cooking term meant to heat something up, possibly with oil to cook it and maybe brown it. You could stir fry with water but I think that's more like sautéing.

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"Boiling" for water is when the vapor pressure of the liquid, equals the ambient air pressure. Water at any pressure has a vapor component, it just happens to be a lower pressure typically than ambient pressure. That's why you can leave a glass of water out, and eventually it will evaporate.

Oil's have a vapor pressure also, it just happens to be much higher than water. We boil oil all the time, as this is typically how it is refined and processed, even vegetable oils. However some oils decompose, before they get to their boiling point.

Frying as others have said is when you boil water out of food, using hot oil.

If you put water under a high enough vacuum, even at room temperature the vapor pressure will equal the ambient temperature and it will boil. In cities like Denver you have to adjust baking and cooking because water actually boils lower than the typical 212F/100C

They definitely do not boil the oil to refine it as the smoke point is so much lower it wouldn't make any sense. They heat the oil to like 180f and add an alkaline substance. There are some steaming processes later on but they stay about 100f (400-450f steam temp) below the actual boiling point of the oil and this process deodorizes the oil.

Hexane extraction using fractjonal distillation was a common method for vegetable oil production. So yes in part the oil will be boiled. It's not what a pot on your stove would look like, and takes into account vapor pressures differences, but it boiled would be an accurate description.

Signed, a Chemical Engineer.

The other responses have answered your question, but I wanted to mention this: You can cook in oil without boiling it, and you can cook in hot water without boiling it as well (like when you're using a sous-vide).

In both cases the liquid is being used to impart heat to the food.

Boiling point of oil is much higher than water. This means when we cook something in oil it can be subjected to much hotter temperatures than water. The sizzling and popping of things in fry oil is from water boiling away.

Same principle with pressure cookers and air fryers - cook it with a medium much much hotter than boiling water can