To “second” something means to be in support of a proposed idea or motion.

second某事的意思是支持一个提议或想法。

Formally, in a meeting when someone suggests or proposes an idea, there needs to be a “second” (someone else who supports the motion) for discussion to take place that results in a vote. Without a “second” the idea or motion dies and is not considered.

正式地说，在会议上，当有人提出一个建议或想法时，需要有第二个人（支持该动议的其他人）进行讨论，然后进行投票。没有second的想法或动议则不被考虑。

Informally, if people are just talking in a group and someone has an idea or makes a point about any particular subject, someone else in the group may say, “I second that”, meaning that he/she supports the idea and agrees with what was said.

非正式地说，如果人们只是在一群人中交谈，有人对任何特定的主题有一个想法或提出一个观点，这个群体中的其他人可能会说，I second that，意思是他支持这个观点并同意所讲的内容。

例句：

- How about pizza for dinner?

-今晚吃披萨怎么样?

- I second that!

-我同意。

The motion was proposed by the club's chairwoman and seconded by the secretary.

该动议由俱乐部主席提出，由干事附议。

- I could use a drink.

-我想喝杯饮料。

- I'll second that.

-我赞成。

（来源：每日学英语公众号）