The vocabulary of any language doesn't remain the same, but changes constantly. New notions come into being, requiring new words to name them.
A neologism is a word, a term, or a phrase which has been recently created- often to apply to new cultural concepts. Neologisms are specially useful in identifying inventions, new phenomena or old ideas which have taken on a new cultural context.
Neologism is a term which refers to any new lexical unit, the novelty of which is still felt.
Neologisms are words which have recently appeared in the language.
e.g. capitalism, communism, proletariat, automat, telegraph, telephone, aviation, etc.