What is an "El Niño" weather pattern?

El Niño (/ɛl ˈniːnjoʊ/ el NEEN-yoh, Spanish: [el ˈniɲo]; lit. 'The Boy') is the warm phase of the El Niño–Southern Oscillation (ENSO) and is associated with a band of warm ocean water that develops in the central and east-central equatorial Pacific (approximately between the International Date Line and 120°W), including the area off the Pacific coast of South America.