What do you understand by the phenomenon of ENSO?

‘ (i) Normally, when the tropical eastern south pacific ocean experiences high
pressure, the tropical eastern Indian ocean experiences low pressure.
(ii) But in certain years, there is a reversal in the pressure conditions and the eastern pacific has low pressure in comparison to the Indian ocean.
(iii) This periodic change in pressure conditions is known as southern
Oscillation or SO.
(iv) The difference in pressure over Tahiti, in the pacific ocean and Darwin in northern Australia is computed to predict the intensity of the monsoon.
(v) A feature connected with the So is the El Nino, a warm ocean current
that flows past the peruvian coast, in place of the cold peruvian current every 2 to 5 years.
(vi) The change in pressure conditions are connected to the El Nino. Hence,
the phenomena is referred to as ENSO (EI Nino Southern oscillations).