Tabs in Salesforce help users view the information at a glance. It displays the data of objects and other web content in the application.
Custom object tabs display data related to custom objects. These tabs look and function just like standard tabs.
Web tabs allow you to embed external web applications and content within the Salesforce window.
Visualforce tabs allow you to embed Visualforce pages.
Lightning Component Tabs
Lightning Component tabs allow you to add Lightning components to the navigation menu in Lightning Experience and the mobile app.
Lightning Page Tabs
Lightning Page tabs allow you to add Lightning Pages to Lightning Experience and the mobile app.
If the tab visibility is Default On, it would appear on the top bar with other visible tabs.
If the tab visibility is Default Off, then the user will still be able to access the tab by clicking on the “+” symbol at the end of all visible tabs on the top bar.
If the tab is hidden, it will neither be visible on the top bar nor by clicking on the “+” symbol.
However, users can edit this according to their preferences.