Not really a slang term (that I am aware of). Just humourous because of the direct translation. whichi is "octopus balls"
A famous Osaka, Japan dumpling made of batter, octopus, tenkasu, pickled ginger, konnyaku, and green onion, topped with okonomiyaki sauce, green laver (nori), mayonnaise, and katsuobushi (fish shavings). Making takoyaki requires a takoyakiki, a special frying pan made of cast iron with hemispherical molds.A piece of octopus piece is in the middle of a round flour paste ball which is not 100% cooked.
The direct translation is "octopus balls"
The size of takoyaki are about a mouthful, and nothing more.
Let's chow down on some octopuses balls.....
Her boobs are the size of tacoyaki
Her boobs are the size of takoyaki