ENSO is a geographical phenomena, if we break the term, EN stands for EL NINO and SO stands for Southern Oscillation. ENSO phenomena mostly occurs at the southern hemisphere just right below the equator.
Temprature of Pacific Ocean, the largest body of water on earth, oscillates back and forth from warm temprature to cold temprature and vice versa. This large pool of water gets intensely warm as it exists right at the equator and we all know that the equatorial region receives great amount of sun rays throughout the year.

ENSO can be classified into three phases-
1. Neutral Phase
2. LA NINA Phase
3. EL NINO Phase
.......to be continued

(Phases will be explained in upcoming Posts)