YouTube is a video sharing platform, founded in 2005 by 3 former PayPal employees. It shortly became the most popular social network of this type.
The company is sold to Google in 2006 but the integration with Google’s other tools and platforms starts several years later.
YouTube is still the most popular “free” video sharing network but there are a few others coming fast from behind (Vimeo, DailyMotion, MetaCafe etc.), while other social networks started implementing this as an extra feature (Facebook).