"The key difference between gas and vapor is that gas exists only in one physical state whereas vapor can coexist with another physical state."

A direct quote from this website: http://www.differencebetween.com/difference-between-gas-and-vs-vapor/

A gas is a form of matter that not only flows to conform to the shape of its container but also fills the entire volume of its container and vapor refers to the gaseous state of a substance that is a solid or a liquid at room temperature