A fixed expression meaning the final option when all else has failed. Often used with verbs like 取る, 使う, or 残す.
If the negotiations break down, I intend to take legal action as a last resort.
He asked his parents for help as a last resort.
最後の手段 is a neutral term for the final option when nothing else works, while 苦肉の策 stresses the pain or self-sacrifice behind the desperate choice.
A transparent compound of 最後 (last) + の (possessive particle) + 手段 (means, method).