It's a network hieroglyph, which means malicious smile and evil eyes.

XD is sometimes used as an expression, x as an eye and d as a mouth. More people are willing to accept it as a knowing smile, where X stands for cross eyes and D stands for big mouth.

Extended data:

XD and other network language sources:

The emergence and spread of this language mainly depends on the network crowd and a large number of mobile phone users.

There are rich and vivid emoticons in QQ chat, such as a waving hand instead of "goodbye, a steaming cup means drinking tea." More and more "dialect words" appear in mobile phone short messages.

Network language can spread because it is recognized, which reflects a certain reality and vividly reflects the mood of netizens at that time.

References:

XD (Network Language) _ Baidu Encyclopedia