noun · a legal document or formal written statement (such as a power of attorney, warrant, or commission) giving someone the authority to act on another's behalf

办理房屋买卖手续需要一份经公证的委托书。

noun · a written document authorizing a person to represent or vote for another, especially in a corporate or formal meeting

他无法出席股东大会，因此签署了委托书请人代为投票。