Blaumachen is a verb made up of 'Blau' (blue) and 'machen' (to do or to make) and means 'to skive' or 'to skip work (or school)'.
You're bound to know the feeling: when the alarm rings in the morning and you can't get out of bed. Maybe, just maybe, you decide to have a duvet day instead of going into school or work.
It's unclear exactly where the term comes from, but it perhaps originates from 'Blauer Montag' or 'Blue Monday', traditionally a day when some tradespeople didn't work or didn't want to put full effort in after the weekend.
So how do you use it?
You could say:
Sie hat blaugemacht und ist nicht zur Arbeit gegangen
She skived off and didn't go to work.
Der Schüler möchte heute unbedingt blaumachen.