Adding a new link in the Top Link Bar without creating subsite?

Background

I'm overhauling an existing Sharepoint site. There are three "tabs" in the Top Link Bar. Tab 1 is "Home," Tab 2 is "Labor," and Tab 3 is "Training."

However, when I go to Site Settings -> Site Administration -> Sites and Workspaces, I don't see "Labor" and "Training" appear as Subsites. How is this possible? I thought that to add a new tab to the Top Link Bar one had to create a new subsite.

I know that "Labor" and "Training" in my case cannot be subsites because:

1. They don't appear under the Subsites list in settings


2. When changing the site theme for one tab, the rest align to the same theme (subsites don't do this)

Since they are not subsites, they must be a different kind of site, right?

Questions

I am a beginner and would like to understand:

1. The difference between the types of sites that one can add to the Top Link Bar


2. What type of sites "Labor" and "Training" are, and how to duplicate them


3. Advantages/disadvantages in either case

I'm using Sharepoint 2010. Answers for any of the above three would be appreciated.