炸 is deep-fried, 薯 is potato (also sweet potato), and 條 is a strip, so 炸薯條 is deep-fried potato strip.
Ordering
條 is also the classifier for long thin items, so if for some reason you wanted to order one french fry, you'd specify 一條炸薯條 (in Cantonese, yāt tíu ja syùh tíu) one strip of deep-fried potato strip.
In the more typical case, you'd order 一碟炸薯條 (in Cantonese, yāt dihp ja syùh tíu) one plate of deep-fried potato strips.
Hong Kong cafes serve sandwiches, so why not french fries?