An anachronism (from the Greek ἀνά ana, 'against' and χρόνος khronos, 'time') is a chronological inconsistency in some arrangement, especially a juxtaposition of people, events, objects, language terms and customs from different time periods. The most common type of anachronism is an object misplaced in time, but it may be a verbal expression, a technology, a philosophical idea, a musical style, a material, a plant or animal, a custom, or anything else associated with a particular period that is placed outside its proper temporal domain.

An anachronism may be either intentional or unintentional. Intentional anachronisms may be introduced into a literary or artistic work to help a contemporary audience engage more readily with a historical period. Anachronism can also be used intentionally for purposes of rhetoric, propaganda, comedy, or shock. Unintentional anachronisms may occur when a writer, artist, or performer is unaware of differences in technology, terminology and language, customs and attitudes, or even fashions between different historical periods and eras.

The metachronism-prochronism contrast is nearly synonymous with parachronism-anachronism, and involves postdating-predating respectively.

A parachronism (from the Greek παρά, "on the side", and χρόνος, "time") postdates. It is anything that appears in a time period in which it is not normally found (though not sufficiently out of place as to be impossible).

This may be an object, idiomatic expression, technology, philosophical idea, musical style, material, custom, or anything else so closely bound to a particular time period as to seem strange when encountered in a later era. They may be objects or ideas that were once common but are now considered rare or inappropriate. They can take the form of obsolete technology or outdated fashion or idioms.

A prochronism (from the Greek πρό, "before", and χρόνος, "time") predates. It is an impossible anachronism which occurs when an object or idea has not yet been invented when the situation takes place, and therefore could not have possibly existed at the time. A prochronism may be an object not yet developed, a verbal expression that had not yet been coined, a philosophy not yet formulated, a breed of animal not yet evolved or bred, or use of a technology that had not yet been created.

A metachronism (from the Greek μετά, "after", and χρόνος, "time") postdates. It is the use of older cultural artifacts in modern settings which may seem inappropriate. For example, it could be considered metachronistic for a modern-day person to be depicted wearing a top hat or writing with a quill.

Works of art and literature promoting a political, nationalist or revolutionary cause may use anachronism to depict an institution or custom as being more ancient than it actually is, or otherwise intentionally blur the distinctions between past and present. For example, the 19th-century Romanian painter Constantin Lecca depicts the peace agreement between Ioan Bogdan Voievod and Radu Voievod—two leaders in Romania's 16th-century history—with the flags of Moldavia (blue-red) and of Wallachia (yellow-blue) seen in the background. These flags date only from the 1830s: anachronism promotes legitimacy for the unification of Moldavia and Wallachia into the Kingdom of Romania at the time the painting was made.^{[citation needed]}