Potassium hydroxide, koh, is considered a in an acid-base reaction because it a hydrogen ion to/from the other reactant.

Potassium hydroxide, KOH, is considered a BASE in an acid-base reaction because it ACCEPTS a hydrogen ion from the other reactant.

According to Brønsted–Lowry acid–base theory, Base is a specie which accepts proton (H⁺) while, Acid is a specie which donate proton.

Bases may contain a negative charge or lone pair of electrons, while, Acids contain positive charge or a neutral atom with incomplete octet.

In given statement KOH is acting as a base because it contains a negatively charged hydroxyl group which can accept proton from a acid, i.e.

                                    KOH    →     K⁺  +  OH⁻

Reaction of OH⁻ with any acid,

                         K⁺    +   OH⁻  +   HCl      →       H₂O   +   KCl