The potential required to lift an electron from the ground state to some higher state is called excitation potential.
If the energy supplied to an electron is such that the electron is lifted from its ground state to one of the higher allowed orbits, the atom will be excited and the energy supplied is called excitation energy or excitation potential. The excitation energy is equal to the difference of energies of the electron in the two orbits.
E = hν = E2 – E1
The potential required to completely remove an electron from the atom is called ionization potential. Or “The potential required to eject an electron from ground state to infinity is called ionization potential.
If the energy supplied to an electron is such that the electron is lifted from its ground state to an orbit at infinity, the atom is said ton ionized, and the energy supplied is called the ionization energy or ionization potential. The energy is so much that the electron disengages it from the atom but its kinetic energy outside the atom is zero.