Top definition
The third monday of January that is the U.S. Federal Holiday for milk.
Milk day fell on 1/16/2012.

"what's MLK day? is it milk day? I think they forgot the "I" in milk #confused #????" - @AlexEbinger via twitter

"What is this MLK Day I'm reading about? Milk day?" - @Koji_Katsuragi via twitter
by slartbarg January 16, 2012
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