What are bases and alkalies?

Oxides and hydroxides of metals and metal like radicals (e.g., NH4⁺ ions) are called bases. Bases ionise to give OH^- ions in aqueous solution. Bases may be soluble or insoluble in water. The soluble bases are called alkalies. Thus all alkalies are bases but all bases are not alkalies. Examples
NaOH and Cu (OH)₂ both are bases, but, since NaOH is soluble in water, it is an alkali. On the other hand, since Cu (OH)₂ is insoluble in water, it is not an alkali. Other examples of alkalies are KOH, Ca (OH)₂ and NH₄OH.