what is the meaning of......

xD is a "emoticon" people often use in emails and text messages. "Emoticon" means that you express certain emotion with the pictorial combination of symbols and letters instead of writing it out in words.
The most common emoticon is :-), that looks like a smiling face. XD looks like a person with a big laugh and closed eyes.

XD是類似 :-) 的表情符號, 多用在email 裡. XD看來好像一個人在哈哈大笑, 連眼睛都張不開.

other possible answers: http://en.wikipedia.org/wiki/Xd

It mean she or him was very happy.