Commonwealth is a traditional English term for a political community founded for the common good. Historically it has sometimes been synonymous with "republic". The noun "commonwealth", meaning "public welfare general good or advantage" dates from the 15th century.

Originally a phrase (the common-wealth or the common weal – echoed in the modern synonym "public weal" it comes from the old meaning of "wealth", which is "well-being", and is itself a loose translation of the Latin res publica (republic).

The term literally meant "common well-being". In the 17th century, the definition of "commonwealth" expanded from its original sense of "public welfare" or "commonweal" to mean "a state in which the supreme power is vested in the people; a republic or democratic state".

The term evolved to become a title to a number of political entities. Three countries – Australia, the Bahamas, and Dominica – have the official title "Commonwealth", as do four U.S. states and two U.S. territories. More recently, the term has been used to name some fraternal associations of nations, most notably the Commonwealth of Nations, an organization primarily of former territories of the British Empire, which is often referred to as simply "the Commonwealth"