SOUND[no plural]›Sounds in the background are not the main sounds you can hear: background music/noiseI could hear a baby crying in the background.
PERSON[C]›a person's education, family, and experience of life: She came from a middle-class background.
PICTURE[C, U]›the parts at the back of a picture, view, etc which are not the main things you look at: gold stars on a black background
SITUATION[C]›the situation that an event happens in, or things which have happened in the past which affect it: [usually singular]The talks are taking place against a background of economic uncertainty.
in the background›If a person stays in the background, they try not to be noticed.