Русско-англо-русский юридический словарь

alternate director: someone who does the work of a company director when the director is absent (Cambridge Business English Dictionary)

An alternate director is a person appointed to attend board meetings and vote on behalf of a primary director when the latter is unable to do so. (Australian Institute of Company Directors (AICD))

Alternate director. Someone appointed by an existing director, under a company's articles of association, to take their place temporarily at board meetings, or a specific board meeting, when the appointing director cannot attend. An alternate director is a director only temporarily, while acting as alternate. (Practical Law UK)

An alternate director can be given some or all of the powers as the appointing director. They can also have the same obligations as the appointing director. (asic.gov.au)