A tab app is used on Facebook and can be used to create a contest, event, add your Twitter feed or add photos. These tab apps can be found to the left of your profile picture underneath the cover photo. Here is an example of the tab apps pulled down to show the full layout on the new Timeline layout:
Tab apps can be rearranged but Facebook only allows a total of 12 to be used and 3 is the max number that can shown on the first row without clicking the dropdown. The best ways to use tab apps is to use them to show other social media platforms such as Pinterest and Twitter or even Instagram. Events and contests are another option for the apps. Tab apps are a great way to engage your followers and to push useful content onto your page.
When using a tab app, you can use programs such as Woobox. This article on Woobox and Pinterest as a tab app explains how the app can be used and the other installations that can be placed on a Facebook page.
Here is our whitepaper on the new Timeline Features for Facebook that shows the tab apps.
Once you have a few tab apps and you are using them for events, contests or adding other social media platforms, you will see the engagement from your followers go up.