So, a succinct explication would be Pop Culture derives from the popular cultural themes in one group of peoples, usually a nation. These themes range and vary with all that on the surface of the mainstream media. Examples are movies, music, current events, fashion, and other phenomena. The internet has definitely played one of the biggest roles with the impact it has had on society by providing the fastest and broadest medium for all this things to be transmitted to everyone and anyone. With out the internet, there also wouldn't be a fairly new addition to the themes of pop culture: Memes.
Which has certainly provided most of us with great sources of entertainment.
I really liked this other pages:
I like the way that last link sums it up nicely:
"Popular culture has been defined as everything from "common culture," to "folk culture," to "mass culture." While it has been all of these things at various points in history, in Post-War America, popular culture is undeniably associated with commercial culture and all its trappings: movies, television, radio, cyberspace, advertising, toys, nearly any commodity available for purchase, many forms of art, photography, games, and even group "experiences" like collective comet-watching or rave dancing on ecstasy. While humanities and social science departments before the 1950s would rarely have imagined including anything from the previous list in their curricula, it is now widely acknowledged that popular culture can and must be analyzed as an important part of US material, economic and political culture. "Pop culture" is also one of the US' most lucrative export commodities, making everything from Levi's jeans to Sylvester Stallone movies popular on the international market. "These group experiences they mention, such as rave parties, and fads such as Planking:
Certainly fall under pop culture.
At the end of the paragraph they mention how Pop Culture is one of the U.S's biggest exports. Like wise, as the U.S's counter part in Asian, Japan also exports and sells gargantuan amounts of "pop culture," most prominent in other Asian countries, but also big in the U.S, such as video games and anime/manga. May be some music...but in ALL absolute honesty, Americans don't consider Japanese pop music to be that great, unless they are "otakus" (Which Otakus from the US are inherently different than Otakus in Japan) or REALLY just love Japan.
The way I like to think about pop culture is the collective preferences of the masses, since when boiled down to the individual, their unique preferences will be very different from every one else's, but when all added at ones, they will lose their singularity and become the huge mess of pop culture out there.
I personally dislike most pop culture as most of it is painful to bare, hear or watch and choose to enjoy what I want, when I want, and if it happens to coincide with pop culture then it's on mere coincidence. This is why I feel like I'm an 80 year old man.
As for pop culture in social media, there's Youtube.com, Facebook pages, and all sorts of other links to follow. Here's one that apparently keeps up to date:
For Japanese craziness of pop culture, Dannychoo.com would be your best gateway.