Wall of Sound

Phil Spector's "Wall of Sound" was created by having several musicians play the same part in unison (for example: five lead guitars instead of one), and running the signal through an echo chamber as well. Mr. Spector would take a song written for a few musicians and arrange it for as many as a full orchestra, often times using instruments not normally associated with the type of song being recorded.

His major driving premise was that no single instrument should dominate the recording. Rather, that they should all blend together into what could only be described as a "wall of sound."

See also:
http://www.jeffosretromusic.com/spector.html
Phil Spector's Wall of Sound