To choose not to participate in something
决定不参加某组织，脱离
“give individual schools the right to opt out of the local educational authority”(&b{Newsweek})
“给予每一学校有脱离地方教育行政体系的权利”(&b{新闻周刊})
choose to participate
决定参加
the database would not include a person's name unless he opted in.
除非决定参加，否则数据库将不录入姓名。
choose not to participate in or carry on with something
决定不参加；退出
the treaty gives any country the right to &B{opt out of} a single currency.
条约赋予任何国家退出单一货币的权利。