Undeserved describes something you got but had not earned — and the word says that is unfair. It works both ways, which surprises students. Undeserved criticism, undeserved blame, an undeserved punishment: you are being treated badly for no good reason, and the speaker is on your side. But equally: undeserved praise, an undeserved reputation, an undeserved win — you got something good you had not earned, and now the word is a quiet criticism. So the sentence around it tells you whether it is a defence or a complaint. It is an adjective that lives in front of nouns; you rarely say "the criticism was undeserved" — though actually that is perfectly good English and quite elegant, just less common. The feel is a step above everyday talk: it belongs to writing, to speeches, to sports reporting ("an undeserved defeat"), to anywhere someone is weighing what is fair. In ordinary speech people say "he didn't deserve that" instead, which means the same and sounds warmer.