What is meant by electrostatic energy density ?

Explanation

The energy stored per unit volume of space is defined as energy density `mu_(E) = (U)/("Volume")`
From equaiton `mu_(E) = (1)/(2) ((epsi_(0)A))/(d) (Ed)^(2) = (1)/(2)epsi_(0) (Ad) E^(2) ` or ` mu_(E) = (1)/(2) epis_(0) E^(2)` .