MCW abbreviates "Man Crush Wednesday." When used, it is preceded by a hash sign and a person writes about a man whom he or she holds in admiration.
The hashtag #MCW is not only used on Facebook, but also on other popular social networks such as Twitter and Instagram. It is a close variant of #WCW, which stands for "Woman Crush Wednesday." When #WCW is used, a person writes about a woman that he/she greatly admires.
There is a hashtag for each day of the week. Examples of these hashtags are #TT for Tuesday, #TBT for Thursday and #FBF for Friday. The hashtag #TBT is generally known to have started the others.