a government organization that is responsible for things such as the safety of important politicians and for preventing secret information being discovered by possible enemy countries

The press reported that he was paid more than $700,000 by the British Secret Service for sharing classified information. 报刊报道说英国情报机构付给他70万美元作为泄露机密文件的回报。

in the US, an organization that is responsible for protecting important politicians

The Secret Service has a responsibility to protect the President from harm. 特勤局有保护总统不受伤害的责任。