You may of heard of the use of the word 'precedent', meaning "thing or person that goes before another". Specifically in law, "a judicial decision which serves as a rule for future determinations in similar or analogous cases". Another example would be in the description of the Wright Brothers' 1903 flight. When that flight took place there was no precedent they could rely on to suggest that the combination of factors that lead to the success of that flight would be successful. Therefore the succes of that flight was unprecedented.
To figure out what 'unprecedented' means you have to have a look at its etymology.
early 15c., preceden, "lead the way; occur or exist before, go before in order of time," from Old French preceder and directly from Latin praecedere "to go before," from prae "before" (see pre-) + cedere "to go".
From an examination of the frequency of use of the terms 'precedent'
and 'unprecedented' you can agree that it has become a buzzword.
Buzzword: also buzz word, 1946, from buzz (n.) + word (n.). Noted as Harvard student slang for the key words in a lecture or reading. Note its level of useage: