The Plaza de Armas (Literally "Weapons' Square") is the name for the main square in many Latin American cities. In Mexico this space is known as El Zócalo, and in Central America as Parque Central (Central Park). While some large cities have both a Plaza de Armas and a Plaza Mayor, in most cities those are two names for the same place.
Most cities constructed by the Spanish Conquistadores were designed on a standard military fashion based on a grid pattern, taken from the Roman Castrum, of which one of the blocks would be left vacant to form the Plaza de Armas. It is often surrounded by governmental buildings, churches, and other structures of cultural or political significance. The name derives from the fact that this would be a refuge in case of an attack upon the city, from which arms would be supplied to the defenders. (See also Huamanga Archos).
Read more about Plaza De Armas: Main Examples of Plaza De Armas in The Hispanic World