
I came across this at a Yoshinoya and I've never seen this before on a menu. I can't figure out what this is supposed to mean; all I can infer from the pricing is that maybe it's a size in between 並 and 大.

I came across this at a Yoshinoya and I've never seen this before on a menu. I can't figure out what this is supposed to mean; all I can infer from the pricing is that maybe it's a size in between 並 and 大.
In 牛丼{ぎゅうどん} ("beef bowl"), 「アタマ」 refers to the toppings that are placed over the rice. In other words, it refers to the stewed beef and onion.
Here, 「アタマ」 refers to the particular size of gyudon consisting of regular-size rice and large toppings, resulting in a "size" between 「並{なみ}」(regular) and 「大盛{おおもり}」(large) in the total amount of food served. This should explain the pricing for アタマ in the photo above.
Please also note that the "official" size name used at Yoshinoya is 「アタマの大盛」.
Hope all this makes sense. It is a fairly popular gyudon size now as it gives you extra beef without all that extra rice to go with it like 大盛 does.
"Big head (= extra toppings) on top of the regular-size rice", so to speak.
Yoshinoya sold 5 million bowls of アタマの大盛 in no time.
