An El Niño describes a period where the western Pacific Ocean contains abnormally warmer waters and the eastern Pacific contains abnormally cold water.  This results in climate changes for continents near the Pacific, and even continents as far as Africa. El Niño's climactic impacts range from floods to droughts. El Ni
ño was named by local Spanish fisherman since they noticed warmer waters came around Christmastime. The El Niño/La Niña yearly time scale ranges from 2-7 years and a more general term to describe an El Niño/La Niña is ENSO (El Niño-Southern Oscillation)

Figure 1- Diagram of Sea Surface depth relative to their normal depth (From http://www.solcomhouse.com/elninolanina.htm) 

Works Cited:
Climate Prediction Center Internet Team.  The ENSO Cycle.  19 Dec. 2005.   <http://www.cpc.noaa.gov/products/analysis_monitoring/ensocycle/enso_cycle.shtml>.
The International Research Institute for Climate and Society.  Overview of ENSO.  27 Mar 2008. <http://iri.columbia.edu/climate/enso/societal/impact/index.html>.
Paul Simmons.  El Niño is back, bringing droughts, floods, crop failures and social unrest. 13 Jul 2009. <http://www.timesonline.co.uk/tol/news/world/us_and_americas/article6695339.ece>.
Kump, Lee R,  Kasting, James F, Crane, Robet G.  The Earth System.  Upper Saddke Ruverm New Jersey: Person Education, Inc., 2010.