A chemical solvent is any solution in which another chemical (the solute) can be dissolved, creating a solution. Solution is an umbrella term that can apply to nearly any liquid product on the market, though it can also take solid, gas, and supercritical fluid forms.
Solvents, however, are strictly liquids. They are technically defined as liquids in which solids will dissolve, which is why so many companies need solvents to make their products. Otherwise, it would be difficult to impossible to mix certain ingredients in such a way as to create a true solution.
Water is the most common solvent on Earth and is used in a wide range of applications. However, often you need more specialized ingredients to create your formulas. These include – but aren’t limited to – ethanol and methanol, acetone, toluene, hexane, benzene, and more. Solvents may be used as a means of diluting products as well.