Opaque move
Moving a window with its contents visible for the whole drag instead of as an empty outline, a luxury early window managers switched off out of respect for the CPU.
The first generation of X window managers did not move windows, they moved rectangles. Grab a title bar and twm drew an outline in XOR straight onto the root window, dragged that outline after the mouse, and put the window in place only when the button was released. For the duration it held a grab on the whole server so no other program could draw over the lines, which is why the rest of the screen froze while you dragged. Moving the actual window would have meant a stream of Expose events to programs without backing store, and a 68020 had no time for that.
The alternative was called opaque move: the window comes along, solid, and whatever was underneath gets repainted afterwards. twm offers OpaqueMove as an option, and fvwm compromised with OpaqueMoveSize, a percentage of the screen area below which windows move solid and above which they turn back into outlines. Windows 95 dragged outlines until the Plus! pack added "show window contents while dragging", which became standard in Windows 98. Compositing window managers made the question go away: a window is a texture, and moving a texture costs nothing.