A neologism is word, term, or phrase which has been recently created ("coined") - often to apply to new concepts, or to reshape older terms in newer language form. Neologisms are especially useful in identifying inventions, new phenomena, or old ideas which have taken on a new cultural context.
Neologisms are by definition "new," and as such are often directly attributable to a specific individual, publication, period or event. The term "neologism" was itself coined around 1800; thus for some time in the early 19th Century, the word "neologism" was itself a neologism. It can also refer to an existing word or phrase which has been assigned a new meaning.
Neologisms tend to occur more often in cultures which are rapidly changing, and also in situations where there is easy and fast propagation of information. They are often created by combining existing words or by giving words new and unique suffixes or prefixes. Those which are portmanteaus are shortened. Neologisms can also be created through abbreviation or acronym, by intentionally rhyming with existing words, or simply through playing with sounds.
Neologisms often become popular by way of mass media, the Internet, or word of mouth. Every word in a language was, at some time, a neologism, though most of these ceased to be such through time and acceptance.
Neologisms often become accepted parts of the language. Other times, however, they disappear from common usage. Whether or not a neologism continues as part of the language depends on many factors, probably the most important of which is acceptance by the public. Acceptance by linguistic experts and incorporation into dictionaries also plays a part, as does whether the phenomenon described by a neologism remains current, thus continuing to need a descriptor. It is unusual, however, for a word to enter common use if it does not resemble another word or words in an identifiable way. (In some cases however, strange new words succeed because the idea behind them is especially memorable or exciting). When a word or phrase is no longer "new," it is no longer a neologism. Neologisms may take decades to become "old," though. Opinions differ on exactly how old a word must be to no longer be considered a neologism; cultural acceptance probably plays a more important role than time in this regard.