For the Wikipedia guideline, see Wikipedia:Avoid neologisms.
A neologism 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.
Etymology: Greek νεολογισμός [neologismos], from νέος [neos] new + λόγος [logos] word, speech, discourse + suffix -ισμός [-ismos] -ism
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).

Changing culture
After being coined, neologisms invariably undergo scrutiny by the public and by language prescriptivists to determine their suitability to the language. Many are accepted very quickly; others attract opposition. Language experts (not linguists) sometimes object to a neologism on the grounds that a suitable term for the thing described already exists in the language. Non-experts who dislike the neologism sometimes also use this argument, deriding the neologism as "abuse and ignorance of the language.". Nevertheless if the public continues to use the term, it eventually sheds its status as a neologism and enters the language even over the objections of language experts.

Cultural acceptance
Newly created words entering a language tend to pass through stages that can be described using the following:

Unstable - Extremely new, being proposed, or being used only by a very small subculture (also known as protologism).
Diffused - Having reached a significant audience, but not yet having gained widespread acceptance.
Stable - Having gained recognizable and probably lasting acceptance. Evolution of neologisms
For a list of topically arranged protologisms (very-recently-coined terms), see Wiktionary:List of protologisms by topic.

Sources of neologism
Words or phrases created to describe new scientific hypotheses, discoveries, or inventions. Examples:

beetle bank (early 1990s)
black hole (1968)
laser (1960)
meme (1976)
prion (1982)
radar (1941) Science
Concepts created to describe new, futuristic ideas. Examples:

ansible (1966)
Dyson sphere (circa 1960)
flux capacitor (1985)
hyperspace (1934)
lightsaber (1977)
Metaverse (1992)
replicant (1982)
Ringworld (1971)
robotics (1941) Science fiction
See "Neologisms in literature" topic below.

Literature more generally
Words or phrases created to make some kind of political or rhetorical point, sometimes perhaps with an eye to the Sapir-Whorf hypothesis. Examples:

blue state/red state/swing state (c. 2000)
Californication (1970s)
Chindia (2004)
corporatocracy
Dixiecrat (1948)
dog-whistle politics (1990)
fauxtography (2005)
genocide (1943)
heterosexism (1979)
homophobia (1969)
Islamophobia (1991)
meritocracy (1958)
NASCAR dad (2004)
political correctness (1970)
pro-choice (1975)
pro-life (1961)
Republicrat (1985)
sie and hir (pronouns)
soccer mom (1992)
Islamofascism (2001)
glocalisation Politics
Words or phrases evolved from mass media content or used to describe popular culture phenomena (these may be considered a variety of slang as well as neologisms). Examples:

badonkadonk
blog
jumping the shark
posterized (Note however that this word has also existed for some time as a term for an image-editing technique; its neologistic sports usage is completely unrelated.)
prequel
queercore
wardrobe malfunction
Internet
webinar (web-based seminar)
From "d'oh" to "cromulent" - many culturally-significant phrases from The Simpsons are now in common use. Pop-culture
Genericised trademarks. Examples:

aspirin
crock pot
laundromat
linoleum
etc. Commerce & advertising
Words or phrases created to describe new language constructs. Examples:

aptronym (2003; popularized by Franklin Pierce Adams)
backronym (1983)
protologism (2005)
retronym (popularized in 1980)
snowclone (2004) Linguistics
Miscellaneous sources. Examples:

nonce words — words coined and used only for a particular occasion, usually for a special literary effect. Other
By contrast, a paleologism is (in this context) a word or phrase that is alleged to be a neologism but turns out to be a long-used (if obscure) term. An example is "truthiness" (which was "re-coined" as an ironic usage by Stephen Colbert).

A note about paleologisms
Many neologisms have come from popular literature, and tend to appear in different forms. Most commonly, they are simply taken from a word used in the narrative of a book; a few representative examples are: "grok" (to achieve complete intuitive understanding), from Stranger in a Strange Land by Robert A. Heinlein; "McJob", from Generation X: Tales for an Accelerated Culture by Douglas Coupland; "cyberspace", from Neuromancer by William Gibson. Sometimes the title of the book will become the neologism, for instance, Catch-22 (from the title of Joseph Heller's novel). Also worthy of note is the case in which the author's name becomes the neologism, although the term is sometimes based on only one work of that author. This includes such words as "Orwellian" (from George Orwell, referring to his novel Nineteen Eighty-Four) and "Ballardesque" (from J.G. Ballard, author of Crash). Kurt Vonnegut's Cat's Cradle was the container of the Bokononism family of nonce words. Another category is words derived from famous characters in literature, such as "quixotic" (referring to the titular character in Don Quixote de la Mancha by Cervantes), a "scrooge" (from the main character in Dickens's A Christmas Carol), or a "pollyanna" (from Eleanor H. Porter's book of the same name).
Lewis Carroll's poem "Jabberwocky" has been called "the king of neologistic poems" as it incorporated some dozens of invented words. The early modern English prose writings of Sir Thomas Browne are the source of many neologisms as recorded by the OED.

Quotation

Buzzword
Daffynition
Doublespeak
Dr. Seuss, author and renowned creator of neologisms
Dysphemism
Eponym
Etymology
Euphemism
Jargon
Newspeak
Malapropism
Neologistic aesthetics
Nonce word
Onomatopoeia
Portmanteau
Propaganda
Retronym
Siamese twins (English language)
Sniglet
Word formation See also

Information

• Wiktionary: Neologisms unstable


• Wiktionary: Neologisms diffused


• Wiktionary: Neologisms stable


• protologism

Wiktionary: Neologisms
Wiktionary: Neologisms unstable
Wiktionary: Neologisms diffused
Wiktionary: Neologisms stable
protologism