current carrying element/wire is phase and 
element at zero potential uses to close the circuit path is 
neutral.

We are generating the power by generator in Three phase 
system. These three phases can be connected in star or 
delta connection. In case of stare connection there is a 
neutral point of three phases. In normal condition the 
voltage and current flow from neutral is zero. But in the 
case of short circuit or during any fault there is flow of 
current and voltage in neutral. Generally the neutral is 
mostly used for protection purpose and in the case of 
single phase and neutral connection, the neutral is used 
for return path.