Chloroethane is treated with alcoholic potassium hydroxide. The product formed is

Dehydrohalogenation[removal of hydrogen halide]

The reactions in which if two reagents are removed from the reactant those reactions are said to be elimination reactions.

In elimination reactions if H⁺  is removed from β-carbon,those reactions are said to be β-elimination reactions.

In β-elimination reaction reaction the formed product is alkene.