What are 'Volatile' and 'Non-volatile' substances?

Volatile substance is those substances that evaporate or sublimates at room temperature. Volatile substances have higher vapour pressures than non-volatile substances kept at the same temperature.

Examples of volatile substances include Alcohol, Mercury, and Gasoline.

Non-volatile substances are those substances that do not readily evaporate into gas under existing conditions. Non-volatile substances exhibit a low vapour pressure and a high boiling point. 

Examples of non-volatile substances include Sugar and Salt.