Back in the good old days, when you wanted to share something, you used email, messaging clients, IRC, the Usenet or forums for that.
Today, sharing is all about sites like Facebook, Twitter, Pinterest or Google Plus where you share pages and services that you like to friends and complete strangers.
Most webmasters maintain one or multiple social media accounts for their sites and share updates on those social sites to spread the word and get some users interested in visiting the site.