What is the meaning of infinity in potential difference???

Dear student,
infinite is considered as reference point in case of electrostatics. It is more like an imaginary point where the net charge =0, so the potential at infinite is zero. The concept of infinite is used to define work done , when a unit positive charge is moved from infinite to a specific point.
as we know,
(work done) /charge = (potential difference) 
$$\begin{gathered} \raisebox{1ex}{$W$}\!\left/ \!\raisebox{-1ex}{$q$}\right.=V_b-V_a \\ where V_a=potential at infinite =0 \\ and V_b = potential at any specific point \end{gathered}$$
Basically, as the potential at infinite is zero, we can directly get the potential of a specific point from this equation.
so, infinity is considered as a reference place that is fixed
Regards,