na-adjective, noun which may take the genitive case particle 'no'
meaningless; incomprehensible; nonsensical
Describes something whose meaning cannot be understood, or that seems absurd or cryptic. Often used as a strong negative comment.
彼の説明は意味不明だった。
His explanation was incomprehensible.
このメール、意味不明なことばかり書いてある。
This email is full of nonsense.
不可解 is more formal and focuses on something being impossible to understand logically, while 意味不明 is a broader, more colloquial term for anything that doesn't make sense.
訳が分からない is a common phrase meaning 'I don't get it at all,' often used subjectively, while 意味不明 can describe the object itself as lacking meaning.
Compound of 意味 (meaning) and 不明 (unclear, unknown). The combination straightforwardly yields 'meaning unclear'.