Faire la grasse matinée is a French expressions that translates literally to “to make the fatty morning” and means “to sleep in” or “to sleep late”.
faire la grasse matinée
to sleep in, to sleep late

Example sentences
Le dimanche je fais la grasse matinée et je me lève à dix heures.
On Sundays I sleep in and get up at 10 o’clock.
Il est rare que je fasse le grasse matinée car je préfère me lever tôt.
I rarely sleep in as I prefer to get up early.
Expression origin
There are two theories for the origin of this expression. One theory relates the Modern French adjective gras (fatty) to the Latin adjective crassus, which can translate to thick, fatty or greasy. Dating from the 16th century, the expression “dormir la grasse matinée” evoqued the idea of staying for a long time “in the depths of sleep”.
Another theory suggests that the expression dates from the 17th century when high-society women were said to have lounged until late in morning in order to gain weight.


