The peso is the monetary unit (coin) of some Spanish-speaking countries. They were once Spanish colonies. They include Argentina, Chile, Colombia, Cuba, Dominican Republic, Mexico, Philippines, and Uruguay.
The word means 'weight' in Spanish, or more loosely 'pound'. It was a coin that originated in Habsburg Spain. Also called Spanish dollar, it became an important international currency. Spain brought it to its colonies and minted many pesos in Mexico and Peru. Later, Spain stopped using this name, but some of the former colonies still use it.
Historically, the peso was eight reales, the real de a ocho. This translates to the well-known English term "pieces of eight". It is known in many countries as the "thaler" or "Spanish dollar". It was used as the model for the original United States dollar and many other coins which were also minted in silver.