Song is that form of entertainment, creativity and expression, in the creation of which people of poor social layers have had immediate access and participation.  Musicologists report that the first songs were created by agriculturers in order to coordinate teamwork and were further used to musically ‘dress' social events, such as weddings and feast, to praise local or national heroes, and, of course, to express love. 

With the passing of time, the foundation of the first cities, and according to the special circumstances in each country, (for example destruction of Smyrna in the case of Greece, World War I or the financial crash in USA) which led large layers of the population to extreme poverty the variety of subjects increased as new elements and hearings were inserted in music.  Rhythm 'n' Blues and Jazz were born in American shacks, while Cuba gave birth to Son, Fado was invented in Portugal, Tango in Argentina and Rebetiko in Piraeus, Greece.

All of the kinds of music mentioned above evolved in an amazingly common way.  At first they were hunted by the musical companies and social establishment, as songs of the underworld, of no artistic value.  In a few decades time they were accepted by the status quo and, in some cases, properly promoted, even became an international success (for instance Buena Vista Social Club).  

The subjects of the songs are common as well; Love Death, Poverty, life's Anxieties and the reaction to all kinds of Authority.  The bohemian way of life of those singers, song writers and musicians, their contempt of money and of all material things in general, and their biological end, that finds them in the margin of society are also common.

Despite the revivals of some of these songs, the musical industry and the MTV fortunately look down to these splendid musical types
leaving them into limbo (better, in peace).  They promote all kinds of light trash, in order to globalize culture, to eliminate diversity of expression (and any other sort of diversity), expecting the whole world to have fun with Britney Spears (poporn).

In all this bombardment there are people that don't feel satisfied with the offer 

and suspect that there's more to music than Britney Spears. The search of what's authentic and genuine ended for me when I heard the first notes of Fragosyriani.

The urban folk song (which in greek is called “laiko tragoudi” – song of the people) all around the world, was created to be the poorer people's life companion.   Greece was lucky enough to have such a diamond that happened (or chose) to remain rough. 
Rebetiko.