Anacrusis

In poetry and music, and by analogy in other fields, an anacrusis (plural anacruses) is a brief introduction.

In poetry, a set of extrametrical syllables at the beginning of a verse is said to stand in anacrusis (Ancient Greek: "pushing up"). The technique is seen Old English poetry, and in lines of iambic pentameter, the technique applies a variation on the typical pentameter line causing it to appear at first glance as trochaic.

In music, an anacrusis (also known as a pickup) is a note or sequence of notes which precedes the first downbeat in a bar in a musical phrase.
The musical term is inferred from the terminology of poetry, where it refers to one or more first but unstressed syllables of a lyrical verse.

The anacrusis is a perceived grouping which is context generated in the individual phrasing of a concrete composition.
The grouping of one or more antecedent tone events to a perceived phrase gestalt may be rhythmically evoked by their temporal proximity to the phrase's first downbeat (perceived phrase onset).
An anacrusis may also be evoked solely metrically (non-rhythmically ), i. e. tonally, that is, without the downbeat perception enforced by a relative long value.

Although the anacrusis is integrated in a musical phrase gestalt (grouped to it), it is not located in the perceived 'body' of the phrase (which is spanning from its first downbeat to its ending beat), but before the phrase (hence the German term "Auftakt").
In this respect -in a sequence of phrases- the anacrusis also may be perceived 'between' two phrases, neither being perceived as part of the ending of a former one, nor being located in the following one.

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