Meaning:

Literally translated as “plus one,” this term is often seen in online chats, where the speaker wants to express that they agree with what others just said. The “one” refers to the speaker.

Example:

A: 明天晚上的音乐会我有票，谁想听？

Míngtiān wǎnshang de yīnyuèhuì wǒ yǒu piào，shuí xiǎng tīng？

I’ve got tickets for tomorrow evening’s concert. Who wants to go?

B: 给我一张吧。

Gěi wǒ yīzhāng ba。

Count me in.

C: +1。

Jiāyī。

Me too.