This is another trick question- kind of. Essentially an application and tab are the same thing. Here's some back history: when Facebook rolled out the new Timeline profile design for business Pages, the term "tab" was forced into extinction and replaced by the word "application." With Timeline, apps (formally known as tabs) have a have a more sophisticated design, looking similar to a content page on a traditional website. In summary, today many people still refer to an application as a tab even though the term "tab" is no longer correct.
care to Ellaborate a little please. or can you share a link where I can read more about this?