Why is Linkedin on my Mac? I did not install it.

I'm using OS X 10.9.3

I opened up the Notification bar today (for the first time). And, I saw there is a list of Linkedin alerts and button to update Linkedin. I have never installed the Linkedin app on my computer, nor do I want it on my computer.

I went to system preferences and updated my privacy settings: there's a Linkedin menu item under "Privacy" and updated the notification settings (to remove Linkedin notifications). But, is some piece of Linkedin code still on my computer?

My question is: What is this? (I know what Linkedin is, but is it an app or what?) and why is it on my computer? I do not want Linkedin on my computer. I never installed the app. It doesn't show up in my "purchases" from the app store. I don't have an iPhone.

How do I get rid of it completely?