Nouns ending in -ment are masculine.
The suffix often marks an action or result derived from a verb.
Is appartement masculine or feminine?
l'appartement
The rule behind it
99.6% of -ment nouns are masculine
In context
Il a trouvé un bel appartement pour Mary.
He found a nice apartment for Mary.
Récemment, j'ai emménagé dans un nouvel appartement.
Recently I moved to another apartment.
Nous déménageons de cet appartement le mois prochain.
We're moving out of this apartment next month.