Drag and drop
Drag and drop is a very powerful, convenient, and intuitive mechanism for doing simple manipulations of objects (files, programs, etc.) in a computer operating system using a mouse and a graphical user interface (GUI). It uses the common metaphor of picking an object up and carrying it someplace. The way that this is done is by clicking and holding the mouse button while it is over the object (that is, the icon or other designator of the object), moving the mouse while still holding the button, and then releasing the button at the destination point. Dragging and dropping is a very versatile operation.
For example, files can be moved from one directory (folder) to another by opening the source and destination directories in "explorer" or "finder" applications, and dragging the file from one place to the other. This actually moves the file (though there are typically other actions that can be performed with other mouse clicks.) For this type of operation, the desktop itself can store files, and files can be moved from an explorer to the desktop and vice-versa. Drag and drop can also be used simply to move things around on the desktop.
Another thing that can be done with this mechanism is deleting a file by dragging it to the "recycle bin" on the desktop.
Another use of this powerful metaphorical operation is to send a file to an application program. If a file is dragged to an application such as an editor or printer, or to the icon for such an application, a typical response is for that application to "open" that file, that is, to edit or print that file. In that case the file is not actually moved; the editor or print application is simply started with that file as its target.
In a few operating systems (MacOS, for example), an application can be dragged to a part of the screen called the "dock" (this is called the "taskbar" in Windows or Linux) to make it inactive, that is, to disconnect it from the window system. This is called "docking" in MacOS. The equivalent operation in Windows or Linux is called "minimizing", and is done by clicking the "minimize" button (the "minus sign") in the upper-right corner.