Just as the title, what is the W in Wワーク?
There is also those U-turn I-turn.....etc
Could you elaborate why is it just a single leter and what is the meaning of it?
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Sign up to join this communityW is pronounced ダブルユー (EDIT: or actually probably more commonly as ダブリュー or even only just ダブル as pointed out by Nanigashi in the comments below), based on the English alphabetic name of the same letter.
Over time the association between the romaji "W" and the ダブル part of ダブルユー/ダブリュー has lead to a custom where any context involving the word double/ダブル can be compactly abbreviated in text form as "W". Often seen in advertising too:
Wバーガー and such.
As you've probably guessed by now, Wワーク(ダブルワーク)simply refers to having two jobs at once.