Mediums are mixtures of the basic paint ingredients that when mixed with the paint just before application change the paint characteristics and allow various artistic effects including faster or slower drying, thicker or runnier paint, and even the inclusion of unusual materials like sand that have texture.
Acrylics in particular are enlivened and empowered by the creative use of mediums. Most artists who tried acrylics and did not enjoy the experience have merely used water as a thinner. That is like trying to oil paint with only turps, limiting. Mediums make the paint exciting to use.
