Forums– Similar to the “Social” tab, but more focused on social forums, mailing lists, and groups to which you belong.
This tab will include order confirmations, receipts, bills, statements, and assorted “program update" messages.
Updates – This contains various "transactional" types of Emails.
This includes sites such as Facebook, Twitter, LinkedIn.
Social – As suggested by the name, this contains Emails from your social networking sites.
This includes special offers, promotional Emails, and newsletters.
Promotions – Most routine marketing Emails route to this tab.
It is the first tab that appears when you view your Gmail Inbox. It will also contain anything that Gmail does not categorize into one of the other tabs.
Primary – This is the main tab that contains correspondences from friends, family, and business contacts.
The new Gmail tabs are available not only in the native Gmail application, but also in the Android and iPhone Gmail apps! Here is the list of the default Gmail Tabs: Each tab will display the number of " new messages" in it, along with the first few names of the recipients.