A neologism (from Greek neo = "new" + logos = "word") is a word that, devised relatively recently in a specific
time period, has not been accepted into a mainstream language. By definition, neologisms are "new", and as such are often directly attributable to a specific individual, publication,
period, or event. The term "neologism" was coined in 1803.1
In psychiatry, the term neologism is used to describe the use of
words that only have meaning to the person who uses them, independent of their common meaning. This is considered normal in children, but a symptom of thought disorder (indicative of a psychotic mental illness, such as
schizophrenia) in adults.
"Yesterday's neologisms, like yesterday's jargon, are often
today's essential vocabulary."
– Academic Instincts, 20014