Independent director is often used interchangeably with the term non-executive director. However, independent directors are those that do not have any significant relationship past or present with the company (such as being a former employee or a major customer) beyond their non-executive role and can have only a limited shareholding or investment in the company.
So while all independent directors have the same role on the board as non-executive directors, not all non-executive directors can be considered independent directors.