What is this called in GUI? A panel that contains tabs

1. What is a tab in user interface?
2. What is tab design?
3. Why are tabs used?

What is a tab in user interface?

In interface design, a tab is a graphical user interface object that allows multiple documents or panels to be contained within a single window, using tabs as a navigational widget for switching between sets of documents.

What is tab design?

The Design tab includes table formatting, cell and table borders, arranging the table on the page, and the size of the table.

Why are tabs used?

Tabs allow you to switch between options in a program, separate documents, or web pages. The currently-selected tab is usually underlined or highlighted in a different color than the other tabs. The interface is designed to resemble the tabs at the top of traditional file folders, as viewed from inside a file cabinet.