The tooltip is a common graphical user interface element. It is used in conjunction with a cursor, usually a mouse pointer. The user hovers the cursor over an item, without clicking it, and a tooltip may appear — a small "hover box" with information about the item being hovered over.
A common variant, especially in older software, is displaying a description of the tool in a status bar, but such descriptions are not usually called tooltips. Another system, on old Mac OS versions, that aims to solve the same problem, but in a slightly different way, is balloon help. Microsoft invented another term, “ScreenTip”, and uses it in its end-user documentation. The tooltip is used for providing an interface between pointer and push button generally.
Demonstrations of tooltip usage are prevalent on Web pages. Many graphical Web browsers display the title attribute of an HTML element as a tooltip when a user hovers the mouse cursor over that element; in such a browser you should be able to hover over Wikipedia images and hyperlinks and see a tooltip appear. Some browsers, notably Microsoft’s Internet Explorer, will also display the alt attribute of an image as a tooltip in the same manner if an alt attribute is specified and a title attribute is not. If a title attribute is also specified, it will override the alt attribute for tooltip content.
The term tooltip originally came from older Microsoft applications (like Microsoft Word 95), which had a Toolbar where moving the mouse over the buttons (the Toolbar icons) displayed these Tooltips, a short description of the function of the tool in the Toolbar.[citation needed] More recently, these Tooltips are used everywhere, not only on Toolbars.
— from Wikipedia, the free encyclopedia