"Drag" is an action idiom common to several [GUI] canons, roughly co-ordinate with, say "[pan]".
It most often appears in discussions of [drag and drop] facilities.

It only takes a few lines of [Tk] to exhibit dragging.  
Here is an example [Michael Kraus] offered in [the comp.lang.tcl newsgroup]:

This demo creates a small window consisting of a single button, 
that can be dragged around on the screen.
Clicking the button quits the program.

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  pack [button .b -text "The Button" -command exit]
  wm overrideredirect . 1

  bind .b <1> {
    set iX0 [expr %X-[winfo rootx .b]]
    set iY0 [expr %Y-[winfo rooty .b]]
    set bMoved 0
  }

  bind .b <B1-Motion> {
    wm geometry . +[expr %X-$iX0]+[expr %Y-$iY0]
    set bMoved 1
  }

  bind .b <ButtonRelease-1> {
    if { $bMoved } break
  }
 
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[[Next up:  exhibit dragging an item around a [canvas].  Check with [CL] if you're in a hurry.]]
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[Category Concept] | [Category GUI]