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

second某事的意思是支持一個提議或想法。

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.

正式地說，在會議上，當有人提出一個建議或想法時，需要有第二個人（支持該動議的其他人）進行討論，然后進行投票。沒有second的想法或動議則不被考慮。

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.

非正式地說，如果人們只是在一群人中交談，有人對任何特定的主題有一個想法或提出一個觀點，這個群體中的其他人可能會說，I second that，意思是他支持這個觀點并同意所講的內容。

例句：

- How about pizza for dinner?

-今晚吃披薩怎么樣?

- I second that!

-我同意。

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

該動議由俱樂部主席提出，由干事附議。

- I could use a drink.

-我想喝杯飲料。

- I'll second that.

-我贊成。

（來源：每日學英語公眾號）