Because they are sniffed or inhaled, these substances are called inhalants. This is a general term that includes all chemicals used in this way. These chemicals can be inhaled because they are volatile - that is, they evaporate when exposed to air. The user commonly pours the substance over a cloth or into a plastic bag and breaths in the vapors. Because most inhalants are solvents, this term is also used to describe these chemicals.
Solvents are just liquids that can dissolve many other substances.
Solvents are produced from petroleum and natural gas. They have an enormous number of industrial, commercial, and household uses as automobile fuels, cleaning fluids, toiletries, adhesives and fillers, and painter thinners and paints. Some have been used as pressurized propellants in aerosols and some anesthetics. Frequently, two or more solvents are found in the same product. Also, other toxic chemicals may be present.