<hardware> To press and release a {button} on a {mouse} or
	other {pointing device}.  This generates an {event}, also
	specifying the screen position, which is processed by the
	{window manager} or {application program}.  On a mouse with
	more than one button, the unqualified term usually implies
	pressing the left-most button (with the right index finger),
	other buttons would be qualified, e.g. "{right-click}".
	{Keyboard} modifiers may also be used, e.g. "shift-click",
	meaning to hold down the shift key on the keyboard while
	clicking the mouse button.

	If the mouse moves while the button is pressed then this is a
	{drag}.

	(1995-03-14)

<operating system> A list from which the user may select an
	operation to be performed.  This is often done with a {mouse}
	or other pointing device under a {graphical user interface}
	but may also be controlled from the keyboard.

	Menus are very convenient for beginners because they show what
	commands are available and make experimentating with a new
	program easy, often reducing the need for user documentation.
	Experienced users however, often prefer keyboard commands,
	especially for frequently user operations, because they are
	faster to use.  In situations such as text entry where the
	keyboard must be used anyway, having to move your hand to the
	mouse to invoke a menu operation is slow.

	There are many different ways of presenting menus but the most
	common are the {menu bar} (with {pull-down menus}) and the
	{context-sensitive menu}.

	The term "menu" tends to be reserved for a list of actions or
	global options, whereas a "{list box}" or other graphical
	{widget} might present any kind of choice.

	See also {menuitis}.

	(1994-12-02)

<mathematics, data> A {directed acyclic graph}; i.e. a {graph}
	wherein there is only one route between any pair of {nodes},
	and there is a notion of "toward top of the tree" (i.e. the
	{root node}), and its opposite direction, toward the {leaves}.
	A tree with n nodes has n-1 edges.

	Although maybe not part of the widest definition of a tree, a
	common constraint is that no node can have more than one
	parent.  Moreover, for some applications, it is necessary to
	consider a node's {daughter} nodes to be an ordered {list},
	instead of merely a {set}.

	As a data structure in computer programs, trees are used in
	everything from {B-trees} in {databases} and {file systems}, to
	{game trees} in {game theory}, to {syntax trees} in a human or
	computer {languages}.

	(1998-11-12)

1. <software> An occurrence or happening of significance to a
	task or program, such as the completion of an asynchronous
	input/output operation.  A task may wait for an event or any
	of a set of events or it may (request to) receive asynchronous
	notification (a {signal} or {interrupt}) that the event has
	occurred.

	See also {event-driven}.

	2. <data> A transaction or other activity that affects the
	records in a file.

	(2000-02-09)

<programming> Redefining in a {child class} a {method} or
	function member defined in a {parent class}.

	Not to be confused with "{overloading}".

	(1996-12-21)