How many types of tabs are there in Salesforce?

Custom tabs display custom object data or other web content embedded in the application.
Custom Object Tabs—For your custom object data. Custom Object Tabs display the data of your custom object in a user interface tab. Custom object tabs look and function just like standard tabs.
Web Tabs—For other web content Custom Web Tabs display any external Web-based application or Web page in a Salesforce tab. You can design Web tabs to include the sidebar or span across the entire page without the sidebar.
Visualforce Tabs—For Visualforce pages Visualforce Tabs display data from a Visualforce page. Visualforce tabs look and function just like standard tabs.
Flexible Page Tabs—For Flexible Pages, to include them in the Salesforce1 navigation menu. Flexible Page Tabs let you add Flexible Pages to the Salesforce1 navigation menu.

There are four types of Tabs (exclusive native tabs): Custom tabs display custom object data or other web content embedded in the application. Custom Object Tabs—For your custom object data. Custom Object Tabs display the data of your custom object in a user interface tab.