's word for the everyone that is no one, the "who" that we ontological
ly are in our everyday lives. If this sounds confusing, don't worry -- it is.
Consider the sentence: "They say it's cold in Alaska." Now zero in on the first word -- "They". Who, exactly, does this refer to? Who is it that says this? Is it you or me, or any one person, or a definite group? It's a bit weird when you think about it for a while. There are similar expressions in German: "Man sagt" means "They say." For this reason, Das Man is often translated as "The They."
The first philosopher (to my knowledge) to build anything on this wierdness was Soren Kierkegaard. He coined the term "the public" to describe it. The public is people in general, but no one in particular. It is the thing that has the majority intrest, the received wisdom, the widespread urge. It is a major force in our lives and thoughts, but no one is it. You can't pick out a single person and say that they are the public. Kierkegaard's conception was a bit more political than Heidegger's, but they say Kierkegaard is the originator of the idea.
Heidegger's big idea was to say that Das Man is actually who we are most of the time. Most of us are so "lost" in Das Man that we don't realize it. We flee ourselves, says Heidegger, by hiding in Das Man. Mostly we hide from Death, but it also relieves us of the burden of real discourse (logos), turning it into what Heidegger called idle chatter -- groundless, buzzing talk that focuses on reaching a consensus that doesn't mean anything at all.
Heidegger was big on authenticity -- the process of individuation. But crucially, he said that to flee Das Man was to flee oneself. Das Man is a part of our basic nature -- we need to embrace it, rather than flee it, if we are to become our own. This is a hard thing for me to accept, but I'm beginning to see the truth of it.