noun
Slang term for a person's physical build, often implying a large, sturdy, or imposing frame. Used in casual conversation.
あの人のガタイはすごいね。
That person has an amazing physique, huh.
彼はガタイがいいから、力仕事に向いている。
He has a big build, so he's suited for physical labor.
The exact origin is uncertain, but it may be a slang alteration of 体 (からだ) or related to がっちり (stocky, solid).