The Spanish word Piedad does indeed mean "piety", but my Spanish-English dictionary says that it also means "pity" and "mercy". Piedad is used as a given name because of the Marian advocation Nuestra SeƱora de la Piedad - Our Lady of Pity/Piety.
When translated to English this name literally means "piety", which more or less can be defined as reverence or devotion -- mainly in a spiritual context. Piety itself originates from the Latin "pietas", meaning duty or devotion. Pietas was considered a virtue in Ancient Rome as well as Confucianism. [noted -ed]