You must have noticed t.co showing up in Referral Traffic Report . t.co is a URL Shortener used by Twitter. Any link posted on twitter gets converted in t.co url and any click on that URL gets routed through t.co and hence you see it in your Referral Traffic Report.
In short, t.co means that the visit came via Twitter.
However, in certain cases if a person take a tweet and posts it on their blog, a click on the link in that tweet will be routed though t.co and you will see t.co is as a referral instead of the blog that posted the tweet.
Experience the ease of comfort to load/access your essential SEO software remotely from any part of the globe with cloud virtual desktop by www.CloudDesktopOnline.com with commendable tech-support from www.Apps4Rent.com