Frost is formed by water vapor that freezes directly onto a surface, typically when the temperature of the surface is below freezing (0°C or 32°F).

Here's a breakdown:

* Water vapor: This is the gaseous form of water that is always present in the air.

* Freezing: When the temperature drops below freezing, the water vapor in the air comes into contact with a cold surface (like grass, a windowpane, or a car).

* Crystallization: The water vapor then transforms directly into tiny ice crystals, which stick to the cold surface.

* Frost: The accumulation of these ice crystals creates the white, feathery pattern we call frost.

So, the white substance that forms frost is frozen water in the form of tiny ice crystals.