I found an interesting phrase here on Facebook page,
What is Waifu-Wednesday? Is there such a thing as Waifu-Wednesday?
Yes and no. No Waifu wednesday is not a officially recognized day for waifu's. Yes, it is a commonly used term in the Waifu-owning society.
Right now, Waifu Wednesday is used by people that have a Waifu/Husbando and use Waifu Wednesday as a mid week appreciation point for their Waifu. This is mostly done by spreading the love of their waifu's by posting Moe and or Kawaii pictures of their Waifu/Husbando.
For those not familiar with the term Waifu Check out "where does the term "waifu" come from?"