The Dock is a graphical user interface element on macOS, iOS and iPadOS used to manage applications in the operating system environment. The Dock appears as stage for icons of pinned apps the user has placed there; it can also include Stacks, used for displaying folders, to the right of the line. The Dock can also initiate Mission Control. The color of the Dock can be light or dark, which is managed through Dark Mode settings.
The Dock serves as an application manager, allowing the user to open, close and switch applications. A running application is indicated by a dot underneath it or being shown in the dock on the very right, and clicking on it will bring up the last used window, or app screen, while holding down on it will bring up all the windows of that application layed out in a grid, in a feature called Mission Control (on IPadOS holding on an app icon shows a lot of quick actions). Stacks and folders also come under the Dock. To the right of the line are more icons, known as Stacks (as well as the Trash icon on macOS). When clicked on, these open up fans of up to 10 items, or grids which display all the items in a folder. You can also browse through the folders inside one another in the Stack.