A propellant is a material that is used to move an object by applying a motive force.
This may or may not involve a chemical reaction.
It may be a gas, liquid, plasma, or, before the chemical reaction, a solid.
Common chemical propellants consist of a fuel, like gasoline, jet fuel and rocket fuel, and an oxidizer.
In aerosol spray cans, the propellant is simply a pressurized vapour in equilibrium with its liquid.
As some gas escapes to expel the payload, more liquid evaporates, maintaining an even pressure.