expression
I see; I get it; so that's why
Expression of realization or understanding, often after hearing an explanation. Equivalent to 'Ah, so that's what it is' or 'Now I understand'.
ああ、そういうことか。やっと分かった。
Oh, I see. I finally understand.
彼が遅刻した理由を聞いて、そういうことかと納得した。
When I heard the reason he was late, I thought, 'So that's why,' and was convinced.