Potassium hydroxide  is an inorganic compound with the formula KOH, and is commonly called  caustic potash .

KOH is a prototypical strong base. It has many industrial and niche applications, most of which exploit its caustic nature and its reactivity toward acids. KOH is noteworthy as the precursor to most soft and liquid soaps, as well as numerous potassium-containing chemicals. 

Most commercial samples are ca. 90% pure, the remainder being water and carbonates.  Its  dissolution  in water is strongly  exothermic . Concentrated aqueous solutions are sometimes called potassium  lyes .