A common method for manipulating files (and sometimes text) under a graphical user interface or WIMP environment. The user moves the pointer over an icon representing a file and presses a mouse button. He holds the button down while moving the pointer (dragging the file) to another place, usually a directory viewer or an icon for some application program, and then releases the button (dropping the file). The meaning of this action can often be modified by holding certain keys on the keyboard at the same time.
Some systems also use this technique for objects other than files, e.g. portions of text in a word processor.
The biggest problem with drag and drop is does it mean "copy" or "move"? The answer to this question is not intuitively evident, and there is no consensus for which is the right answer. The same vendor even makes it move in some cases and copy in others. Not being sure whether an operation is copy or move will cause you to check very often, perhaps every time if you need to be certain. Mistakes can be costly. People make mistakes all the time with drag and drop. Human computer interaction studies show a higher failure rate for such operations, but also a higher "forgiveness rate" (users think "silly me") than failures with commands (users think "stupid machine"). Overall, drag and drop took some 40 times longer to do than single-key commands.