Definiton of Social Media ?

I was reading through the topic about conservative people being banned from some social media sites and i noticed this in a reply..

[quote]Best thing to do is stay off all of them and let them dwindle into the darkness. [/quote]

My initial reaction was .. Well isn't SW a social media site? And you're not staying off SW,, You're posting on SW?

But then i thought ok i would ask this question..

[b]What is social media?

What is your definition of social media?

What makes a site a social media site? [/b]

Thoughts anyone?