El NiÃ o-Southern Oscillation ( ENSO in short ) is a term describing a natural event that takes place in the Pacific Ocean . It is also called El NiÃ o and La NiÃ a. El Nino and La Nina are English words for the Spanish words El NiÃ o and La NiÃ a. In Spanish they mean the `` little boy '' and the `` little girl '' . In popular usage , the El NiÃ o-Southern Oscillation is often called just `` El NiÃ o '' .