From The Art and Popular Culture Encyclopedia
A neologism (Greek νεολογισμός [neologismos], from νέος [neos] new + λόγος [logos] word, speech, discourse + suffix -ισμός [-ismos] -ism) is a word, term, or phrase which has been recently created ("coined") — often to apply to new concepts, to synthesize pre-existing concepts, or to make older terminology sound more contemporary. Neologisms are especially useful in identifying inventions, new phenomena, or old ideas which have taken on a new cultural context. The term "e-mail", as used today, is an example of a neologism.
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; so for some time in the early 19th Century, the word "neologism" was itself a neologism.
Neologisms can also refer to an existing word or phrase which has been assigned a new meaning.
In psychiatry, the term is used to describe the creation of words which only have meaning to the person who uses them. It is considered normal in children, but a symptom of thought disorder indicative of a psychotic mental illness such as schizophrenia in adults. Usage of neologisms may also be related to aphasia acquired after brain damage resulting from a stroke or head injury.
In theology, a neologism is a relatively new doctrine (for example, rationalism). In this sense, a neologist is an innovator in the area of a doctrine or belief system, and is often considered heretical or subversive by the mainstream clergy or religious institution(s).