A colloquial expression meaning completely unintelligible or nonsensical (used when something is incomprehensible or gibberish).
専門用語ばかりで、初めて聞く学生にはちんぷんかんぷんだ。
With so much technical jargon, it's gobbledygook to students hearing it for the first time.
彼の説明は早口でちんぷんかんぷんだった。
His explanation was so fast it was gibberish.
この数学の証明はちんぷんかんぷんで、全然分からない。
This math proof is unintelligible; I don't understand it at all.