"Bite the dust" is an English idiom that can refer to a person dying. This idiom can also have a more general — and less morbid — meaning, referring to anything that has failed or succumbed to some negative fate. The phrase "bite the dust" derives its meaning from the fact that someone who either dies or falls on the ground would literally end up biting the dust. Its origins can be traced back to the Bible, and it can be found in literature as far back as the 18th century, although it gained its most popularity from cowboys and Indians in American Western movies and literature.
In most languages, over time, speakers form words into phrases that, through popular use, take on a meaning that's different from their literal definitions. These phrases are known as idioms, and allow people to get their points across in an evocative and expressive manner. Perhaps because death is sometimes considered a taboo or unlucky topic, many idioms exist in the English language that are used to describe it. One of the most popular of these is the phrase "bite the dust."
The phrase "bite the dust" is most often used as a description of a death. It is important to understand that the phrase is a somewhat flippant way of describing circumstances that are clearly very serious. Thus, the context in which the phrase is used is often either humorous or irreverent. As an example of the phrase, somewhat might say, "He was in the prime of his life and then suddenly, just like that, the poor guy bit the dust."
Using it in this way takes some of solemnity out of death, since it's often not a pretty picture to imagine someone literally eating dust. The phrase can also be used to describe something that either falls out of favor or fails completely. In this way, it can be used in the context of non-living things. For example, someone could say, "We fixed the computer three different times, but I think it's finally going to bite the dust."
While the phrase may not have originated there, it is most commonly associated with American Western movies. Those movies would often feature two gunslingers facing off with each other on an unpaved, dirt road to see who would be the fastest to draw his pistol. The losers of these gunfights would be shot, of course, leaving them to fall face down and, in many cases, "bite the dust." Ever since the heyday of the Western in the 1940s and 1950s, the phrase has been extremely popular in American culture.