Meaning:

“表情” means “facial expression,” and “管理” means “management.” “Facial expression management” refers to the repression of expressions related to the emotions felt and their replacement with expressions that are more socially acceptable under the circumstances. It’s often required of entertainers and idols, who are expected to face harsh criticism with a smile and keep a poker face when something unexpected occurs.

Example:

A: 快来看这个视频，漂亮小姐姐吃柠檬。

Kuàiláikànzhègeshìpín,piàoliangxiǎojiějiechīníngméng.

Check out this video. A pretty young lady is eating a lemon.

B: 哇，居然面带微笑，表情管理满分。

Wā,jūránmiàndàiwēixiào,biǎoqíngguǎnlǐmǎnfēn.

Wow, she could do it with a smile. I guess she’s an expert in facial expression management.