Nouns ending in -at are masculine.
The suffix often marks a status or condition.
Is plat masculine or feminine?
leplat
The rule behind it
100% of -at nouns are masculine
In context
Un plat en plastique fondra sur la cuisinière.
A plastic dish will melt on the stove.
Permettez-moi de vous expliquer le plat du jour.
Let me tell you about our special.
Les piles de ma calculatrice sont à plat.
The batteries in my calculator are dead.