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.
Sie hätte bei der Arbeit nicht blaumachen sollen. Jetzt wird sie gefeuert.