Illustrated Glossary of Organic Chemistry

Solubility: The degree to which one substance dissolves in another. Usually expressed as mass of solute per volume or mass of solvent at a specified temperature. Liquids that dissolve in each other in any ratio are said to be miscible. Liquids which have little or no mutual solubility are termed immiscible. A substance which has little or no solubility is termed insoluble.

--video to be added--

Click image to see a video of NH4Cl dissolving in water.
NH4Cl solubility data. The solubility of NH4Cl (the solute)
in water (the solvent) is 37.2 g NH4Cl per 100 g water at 20 oC.

<--- Oil layer

<--- Vinegar layer (acetic acid + water)
The oil and vinegar layers of Italian dressing are insoluble (immiscible).