This is the 2562nd most frequent German word.
wieso
"Why" or "for what reason."
'Wieso' is used as a singular question word to inquire about the reason behind an action.
Wieso hast du das getan?
Why did you do that?
'Wieso' introduces a subordinate clause explaining the reason for the main statement.
Ich verstehe nicht, wieso er so wütend ist.
I don’t understand why he is so angry.
'Wieso' is used in reported speech to inquire indirectly about a reason.