Meaning:

“微信” is “WeChat,” a social networking app with a lot of functions, and “小号” literally means “small account.” Normally, people use their mobile phone number or QQ number to register their WeChat account. Some people, however, register more than one WeChat account so that they can hide their real identity behind certain WeChat accounts or interact with different people via different accounts. The less known or less used WeChat accounts, compared with the more often used one controlled by the same person, are called the “small accounts.” The same applies with WeChat public accounts, which sometimes have “small accounts” attached to them.

Example:

A: 小丽为什么开了个微信小号？

Xiǎolì wèishénme kāi le gè wēixìn xiǎohào?

Why did Xiao Li register another WeChat account?

B: 她假装是个做销售的美女，试探自己的男朋友是否可靠。

Tā jiǎzhuāng shì gè zuò xiāoshòu de měinǚ, shìtàn zìjǐ de nánpéngyǒu shìfǒu kěkào。

She poses as a pretty saleswoman with this account, to see if her boyfriend will stay loyal to her in the face of temptation.