Meaning:

This term, literally translated as “idle fish,” is a homophone for another Chinese word “闲余,” which refers to “things no longer needed.” It is used as the name of an app developed by Alibaba, where people can buy and sell second-hand goods online. Tencent, Alibaba’s competitor, backs a similar second-hand goods trading app called zhuanzhuan (English meaning: circulation), which is less popular.

Example:

A: 我前段时间头脑发热买了一把小提琴，发现根本没时间去学，估计以后也不会去学。

Wǒ qiánduàn shíjiān tóunǎo fārè mǎi le yībǎ xiǎotíqín，fāxiàn gēnběn méi shíjiān qù xué，gūjì yǐhòu yě búhuì qù xué。

I bought myself a violin on a whim, but haven’t got time to learn to play it. Now it seems that I will never learn to play it.

B: 那就闲鱼出了吧。

Nàjiù xiányú chū le ba。

Well, you can resell it on Taobao’s second-hand app.