Today is my birthday. Naturally I am celebrating it by opening cards and presents, eating a bit too much and drinking a lot too much. Birthdays are a time for celebration just about all over the world.
However this is in some ways a sad day. This is the one day of the year that I cannot celebrate another event. The only day of the entire year that you cannot wish me 'a very merry unbirthday'.
In case you can't remember, an 'unbirthday' is celebrated on any day that is not the person's actual birthday. It was invented by Lewis Carroll in his 'Through the Looking Glass' and gave rise to "The Unbirthday Song" in the 1951 Disney film 'Alice in Wonderland.
In the film, Alice encounters the Mad Hatter the March Hare and the dormouse having an unbirthday party and singing "The Unbirthday Song". Alice at first doesn't realise what an unbirthday is and when the Mad Hatter explains, she realises it is her unbirthday as well, and receives an unbirthday cake from the Mad Hatter.
An 'unbirthday' is a neologism. This may be defined as a newly coined term, word, or phrase, which may be in the process of entering common use, but has not yet been accepted into mainstream language.
You learn something every day, especially on your unbirthday - speaking of which, I can't wait for my birthday to be over so that I may celebrate my unbirthday.