background

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The ground or scenery located behind something.
• noun The part of a pictorial representation that appears to be in the distance and that provides relief for the principal objects in the foreground.
• noun The general scene or surface against which designs, patterns, or figures are represented or viewed.
• noun A position, area, or situation that is not immediately in one's attention or notice.
• noun Computers The environment in which programs operate that the user does not engage with directly.
• noun The circumstances and events surrounding or leading up to an event or occurrence.
• noun A person's experience, training, and education.
• noun The cultural or social environment in which a person was brought up or has lived.
• noun Subdued music played especially as an accompaniment to dialogue in a dramatic performance.
• noun Sound that intrudes on or interferes with an audio recording.
• noun Low-level radiation, as from radioactive decay, that exists as part of the natural environment.
• idiom (on background) For publication but without specific attribution of the source.
• idiom (on deep background) For publication without any attribution of the source.

from The Century Dictionary.

• noun The ground at the back or behind, as opposed to the front; situation in the rear of those objects, considerations, etc., which engage the attention; subordinate or secondary position in contradistinction to principal or important position; place out of sight: used both literally (of physical objects) and figuratively: as, there were mountains in the background; the true reasons for this action were kept in the background.
• noun Specifically The part of a picture represented as furthest from the spectator's eye: opposed to foreground.
• noun In photography, the plain or decorated screens, properties, etc., placed behind the subject in taking portraits, especially in regular gallery-work, in order to form an appropriate setting in the finished picture.

from the GNU version of the Collaborative International Dictionary of English.

• noun Ground in the rear or behind, or in the distance, as opposed to the foreground, or the ground in front.
• noun (Paint.) The space which is behind and subordinate to a portrait or group of figures.
• noun Anything behind, serving as a foil.
• noun A place in obscurity or retirement, or out of sight.
• noun The set of conditions within which an action takes place, including the social and physical conditions as well as the psychological states of the participants.
• noun The set of conditions that precede and affect an action, such as the social and historical precedents for the event, as well as the general background{5}.
• noun (Science), (Physics) The signals that may be detected by a measurement which are not due to the phenomenon being studied, and tend to make the measurement uncertain to a greater or lesser degree.
• noun (Journalism) An agreement between a journalist and an interviewee that the name of the interviewee will not be quoted in any publication, although the substance of the remarks may be reported; -- often used in the phrase “on background”. Compare deep background.
• noun to make of little consequence.
• noun to remain unobtrusive, inconspicuous or out of sight; -- of people.
• noun (Journalism) the status of an interview which must not be quoted in a publication, even without attribution. Compare background{8}.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun One's social heritage; what one did in the past/previously.
• noun A part of the picture that depicts scenery to the rear or behind the main subject; context.
• noun Information relevant to the current situation about past events; history.
• noun A less important feature of scenery (as opposed to foreground.)
• noun computing The image or color, over which a computer's desktop items are show (e.g. icons or application windows).
• noun computing Activity on a computer that is not normally visible to the user
• verb To put in a position that is not prominent

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the state of the environment in which a situation exists
• noun relatively unimportant or inconspicuous accompanying situation
• noun extraneous signals that can be confused with the phenomenon to be observed or measured
• verb understate the importance or quality of
• noun information that is essential to understanding a situation or problem
• noun the part of a scene (or picture) that lies behind objects in the foreground
• noun a person's social heritage: previous experience or training
• noun scenery hung at back of stage
• noun (computer science) the area of the screen in graphical user interfaces against which icons and windows appear