Question

define intensity of sound

Answer 1

it is defined as the power( j/sec ) of sound per unit area(m²),in other words,the amount of energy ( J) per unit time (sec.) per a unit area (m²).
hence its formula= (J/s) /m²
                         =W/m²

Answer 2

The rate at which sound energy is transferred as measured relative to some reference. Loudness determines the intensity of the sound.