The correct answer is:
The rate at which a waves energy flows through a given unit of area
In fact, light intensity is defined as the light power per unit of area:
[tex]I= \frac{P}{A} [/tex]
but the power is the energy carried by the light per unit of time:
[tex]P= \frac{E}{t} [/tex]
this means that the intensity can be rewritten as
[tex]I= \frac{E}{tA} [/tex]
So, it's basically the rate of energy (per unit of time) through a given surface.
