expression, noun-modifying (irregular)
incomprehensible; nonsensical; puzzling
Used prenominally to describe something that makes no sense, is illogical, or cannot be understood. Often carries a nuance of frustration or dismissal.
See also: 訳が分からない
彼は訳の分からないことを言い出した。
He started saying incomprehensible things.
訳の分からない理由で断られた。
I was turned down for some puzzling reason.
A full clause meaning 'I don't understand what's going on' or 'it makes no sense', while 訳の分からない is an adnominal modifier ('incomprehensible ~').
Phrase consisting of 訳 (reason, meaning) + の (possessive particle) + 分からない (negative form of 分かる 'to understand'), literally 'of which the meaning is not understood'.