Impression
An impression is the overall effect of something.
Impression or impressions may also refer to:

Biology
Colic impression, a feature of the gall bladder
Duodenal impression, medial to the renal impression
Gastric impression, a feature of the liver
Impression (dental), a dental procedure
Maternal impression, the effect of maternal mental states on foetal development
Renal impression, a feature of the gall bladder
Suprarenal impression, a feature of the gall bladder

Psychology
First impression
Mental impressions (from the Sanskrit "Samskara")
Mental dispositions or conditioned phenomena (from the Buddhist term Saṅkhāra)

Idiomatic expressions
An idiom is a phrase or a fixed expression that has a figurative, or sometimes literal, meaning.

"To make a good first impression"
"To be under the impression of"

Publishing and advertising
Impression (publishing), a print run of a given edition of a work
Impression (online media), a delivered basic advertising unit from an ad distribution point
Cost per impression, cost accounting tool using in e-marketing
Viewable Impression, a metric used to report on number of distributed ads that were viewable
Impression (software), a desktop publishing application for RISC OS systems
Impressions, the in-flight magazine for British Mediterranean Airways
Impressions Media, an American privately-owned publisher of newspapers

Art
Impression, Sunrise, an 1872 painting by Claude Monet
Post-Impressionism, the development of French art since Manet
Impressions, journal of The Japanese Art Society of America

Music
The Impressions, a music group from Chicago
Impressions (instrumental composition), a jazz standard composed by John Coltrane

Albums
Impression (album), the soundtrack from the anime series Samurai Champloo
Impressions (John Coltrane album), a 1963 album by jazz musician John Coltrane
Impressions (Buck Hill album), a 1983 album by saxophonist Buck Hill
Impressions (Chris Botti album), the 2012 album by trumpeter Chris Botti
Impressions!, a 1959 album by Paul Horn
Impressions (Laura Nyro album), the first compilation retrospective album by Laura Nyro
Impressions (Lunatic Soul album), 2011
Impressions (Mike Oldfield album), a 1980 compilation album by Mike Oldfield released
Impressions (Mal Waldron album), a 1959 album by Mal Waldron
The Impressions (album), a 1963 album

Other uses
Impressions, a form of mimicry practised by an  impressionist (entertainment)
Impressions (Angel novel), a 2003 novel derivative of the television series Angel
Impressions Games, a video game developer

See also
Impress (disambiguation)
False Impression, a 2006 novel by Jeffrey Archer
"First Impressions" (Angel), a 2000 episode of the television series Angel
The Big Impression, a British comedy sketch show
Impressions de France, a 1982 film about France
Impressment, a type of forced military service
Imprint (disambiguation)