Garbage in, garbage out
In computer science, garbage in, garbage out (GIGO) is the concept that flawed, or nonsense (garbage) input data produces nonsense output. Rubbish in, rubbish out (RIRO) is an alternate wording.

The principle also applies more generally to all analysis and logic, in that arguments are unsound if their premises are flawed.

History
It was popular in the early days of computing. The first use of the phrase has been dated to a November 10, 1957, syndicated newspaper article about US Army mathematicians and their work with early computers, in which an Army Specialist named William D. Mellin explained that computers cannot think for themselves, and that "sloppily programmed" inputs inevitably lead to incorrect outputs. The underlying principle was noted by the inventor of the first programmable computing device design:

More recently, the Marine Accident Investigation Branch comes to a similar conclusion:

The term may have been derived from last-in, first-out (LIFO) or first-in, first-out (FIFO).

Uses
This phrase can be used as an explanation for the poor quality of a digitized audio or video file. Although digitizing can be the first step in cleaning up a signal, it does not, by itself, improve the quality. Defects in the original analog signal will be faithfully recorded, but might be identified and removed by a subsequent step by digital signal processing.

GIGO is commonly used to describe failures in human decision-making due to faulty, incomplete, or imprecise data. This sort of issue predates the computer age, but the term can still be applied.

Audiology:
This phrase is also used in audiology to describe the process that occurs at the dorsal cochlear nucleus (DCN) when auditory neuropathy spectrum disorder is present. This occurs when the neural firing from the cochlea has become unsynchronized, resulting in a static-filled sound being input into the DCN and then passed up the chain (hence the "GIGO" nomenclature) to the auditory cortex. The term was coined by Dan Schwartz at the 2012 Worldwide ANSD Conference, St. Petersburg, Florida, on 16 March 2012; and adopted as industry jargon to describe the electrical signal received ay the dorsal cochlear nucleus and passed up the auditory chain to the superior olivary complex on the way to the auditory cortex destination.

GIGO was the name of a Usenet gateway program to FidoNet, MAUSnet, e.a.

See also 

 Algorithmic bias
 Computer says no
 FINO
 Auditory neuropathy spectrum disorder
 Standard error
 Undefined behavior

References 

Computer errors
Computer humor
Computer jargon