An alkali specifically refers to a soluble base that dissolves in water, producing hydroxide ions (OH⁻). This distinguishes alkalis from other bases, which may or may not be soluble in water. Alkalis are typically metal hydroxides, such as sodium hydroxide (NaOH) and potassium hydroxide (KOH), known for their ability to increase the concentration of hydroxide ions in aqueous solutions. In contrast, other bases may not necessarily produce hydroxide ions when dissolved. The characteristic presence of hydroxide ions in solution, giving rise to alkaline properties, is the key feature that differentiates alkalis from other bases.