It was originally thought that an El Niño could only occur in the Pacific Ocean basin, although some scholars are now suggesting that smaller, mini El Niños could also take place in the area around the Indian Ocean. The term El Niño, also referred to as Southern Oscillation, was originally only used to refer to warmer-than-average sea surface temperatures off the west coast of South America.
However, the term El Niño has since been adapted to refer to unusual changes in sea surface temperature anywhere throughout the Pacific Ocean. These abnormalities in the temperature of the sea surface can cause many different temporary effects on the world's weather and climate.
The term El Niño means the boy child in Spanish, and it was first used by fisherman in South America to refer to unusually warm water off the coast. As these changes often occurred around Christmas, the fisherman called them El Niño, which essentially refers to the baby Jesus.
El Niños occur due to the change in surface pressure between the eastern and western halves of the Pacific Ocean, which in turn cause the changes in the surface water temperature. El Niños occur at somewhat regular intervals, with a new one happening about every two to seven years.
Typically, an El Niño event leads to extreme precipitation on the western side of the Pacific, which often causes flooding and other problems on the west coasts of North and South America. However, this also tends to lead to extreme drought on the other side of the Pacific.