げつげつかすいもくきんきん。　Try saying that real fast. No, it’s not a 早口 but in fact an old military/naval song.
It was used after the War by the Japanese Imperial Naval Forces. Sailors were encouraged to give up their weekends to work.

Basically the translation is litrally ‘a week without Saturdays or Sundays, hence the two Mondays and Fridays- a week without a weekend, that is, nothing but work.
Quite simply, All work, no play.

As another weekend flies by, and the long days at work continue, and another Monday rolls around, this phrase is kinda appropriate.

It’s not so commonly said these days, but it can be used when you are super busy at work, and when you work overtime on weekends etc, or don’t get a break from work. It’s kinda cool just to say for fun anyway. It’s nice to roll it off the tongue.

You can read more about the history of it on Wikipedia HERE.

You can listen to the song on Youtube HERE.