The phrase "large fries" means a big portion of French fries, more than the regular size.
Sentences with «large fries»
In the first one, you might eat a Bacon & Cheese Whopper Sandwich with large fries and a medium Coke. (yurielkaim.com)
That was also the year large fries were added and founder Ray Kroc was honored with the Horatio Alger Award (the two events are not related). (topsecretrecipes.com)
Then cut each quarter of the potato in half lengthwise again (so you have potato eighths, which are in the shape of large fries). (melaniecooks.com)