Define electric potential and explain it. Write its $SI$ unit and give its other units.

(N/A) The work done by an external force in bringing a unit positive charge from infinity to a given point in an electric field,without acceleration,is called the electrostatic or electric potential at that point. It is denoted by $V$.
Consider a source charge $Q$ at the origin $O$. Let $P$ be a point at a certain distance from $O$,and $R$ be a point at infinity.
The work done in bringing a unit positive charge from infinity to point $P$ is the potential energy per unit charge.
If $U_P$ is the potential energy at point $P$ and $U_R$ is the potential energy at point $R$,then the electric potential difference between these points is given by $\frac{U_P - U_R}{q}$.
Thus,$V_P - V_R = \frac{U_P - U_R}{q}$,where $V_P$ and $V_R$ are potentials at points $P$ and $R$ respectively.
Since the absolute value of electric potential is not physically significant,only the potential difference is important. By convention,we take the potential at infinity to be zero $(V_R = 0)$.
Therefore,$V_P = \frac{U_P}{q}$.
The $SI$ unit of electric potential is the volt $(V)$,where $1 \ V = 1 \ J/C$. Other units include statvolt $(statV)$ in the $CGS$ system,where $1 \ V = \frac{1}{300} \ statV$.