What did habermas mean by the "public sphere"?

What did Habermas mean by the Public Sphere? Is this concept at all useful for understanding the role of the mass media in contemporary society? Jurgen Habermas by many is considered the most influential thinker in Germany; his ideas of the "public sphere" were developed in the enlightenment era of the eighteenth century and were considered revolutionary. These ideas in some parts of the world are still highly regarded and have become an integral part …

…can be used as a yardstick for measuring the state of the democracy as it has done in many countries across the globe. As a theory however it is not useful if trying to apply this model to today's society, as although it shares some similarities the structure of contemporary society is one run by capitalists and "kings" and because of this fact, equality and freedom of action and speech will never fully be achieved.