Since the electric field in stationary situation have some properities you can introduce a function P(x1,x2,x3) called potential function for which:
dP(x1,x2,x3)/dxi=Ei
where Ei is the component of the electric field in the direction of the unit vector xi (x1,x2 or x3)
the potential difference between two points p1 and p2 in the space is:
P(p2)-P(p1)