There are many definitions of subculture, and the word has been prevalent as long as I can remember. From my brief readings on the matter, it seems the idea was originated by a bunch of sophisticated sociologists as a way to analyze concepts like deviancy and the like that are relatively esoteric and perhaps dated. In modern parlance, subculture often just means "hobby", although often it means "hobby with an attitude".
To define subculture, an explanation of how a subculture relates to a unqualified "culture" must be made. Although it could be somewhat reductionistic, a culture could be defined as all the ways that a group of people manages to live and relate to each other, including of course economic means. A culture is a group of people who share similar means of production. A subculture is then, a group that has the same means of production as a culture, but tends to superficially disguise their participation in that culture, either as a form of rebellion or escapism. A good (if overly stereotypical) example of this would be two young men, who work at a large retailer stocking shelves, and thus both share in the economic system of working for a large organization. However, one identifies with a "cowboy" aesthetic, and goes home to work on his pickup truck and listen to country music. The other thinks of himself as a hippie, and goes home to smoke marijuana and play his guitar. In either case, the activities do not really contribute directly to the material control the people involved have over their life. That is why I would consider the activities involved in to be "subcultural", as opposed to cultural activities.
What I think is most interesting about this is that almost everyone in the United States, on the whole, shares the same culture. Almost everyone in the United States is dependent on large organizations, corporate or governmental, to keep up a sophisticated transportation network that provides them with food and other necessities. Almost everyone will interact with these organizations through mostly impersonal, individual participation in exchange for wages, in order to participate in the money economy. All of American culture, then, is urban culture, because almost everyone, including rural residents, are dependent on urban centers to provide for them. In fact, rural residents are more dependent, since greater distances to be traveled require more fuel and vehicles to obtain necessities.
I say this just to present a reality, not to deny that the moral and intellectual embrace of a subculture can be beneficial to someone, even if just as escapism. Neither do I deny that ideas, values and means of production first embraced by a subculture, such as trying to be somewhat self-sufficient, can not transform or at least influence the culture. I am just trying to point out that subcultures, when they involve nothing else but putting on a different hat, have no real impact on the basis of how people live.