Definition from Wiktionary, the free dictionary
See also El Nino
Alternative forms 
Spanish, meaning “The Little Boy,” referring to the Christ child, as the phenomenon is observed around Christmas time
- An invasion of warm water into the surface of the Pacific Ocean off the coast of Peru and Ecuador every four to seven years that causes changes in local and regional climate, associated with a positive anomaly.
- Additionally, scientists aren’t expecting to be surprised again by El Niño, a warming of the Pacific Ocean that tends to dampen Atlantic hurricane activity. (Houston Chronicle, 5/23/2007)
Related terms 
a global coupled ocean-atmosphere phenomenon