Patat in Dutch are french fries :D
Though in the south (both south NL and Flemish Belgium) they're called "friet", as in "gefrituurd" ("fries" as in "they're fried"). Still, patat is officially Dutch and according to some website 95% of the Flemish people and 100% of the Dutch people know the word.
Same in France with "patate". Funny to notice that the more common French expression for "potato" is "pomme de terre" ("apple of earth"), just like in Dutch!