Definition: start button: a button, labeled “Start. . . ”, that is normally on the screen whenever Windows is running. By clicking on the Start button, you can access application programs and other functions of the computer through the START MENU. If the Start button is not visible, it’s probably because the TASKBAR at the bottom of the screen has been reduced to minimum width. Just move the mouse pointer to where it ought to be, and it will appear. By dragging the taskbar with the mouse cursor, you can restore it to normal width and make it readable again. You can also display the Start menu at any time by pressing Ctrl-Esc. start menu: the menu that is called up by the START BUTTON in the corner of the screen under Microsoft Windows. It leads to all the application software that is installed on the computer. To edit or modify the Start menu, open it with the right mouse button rather than the left button.
Source: Downing, Douglas, et al. Dictionary of Computer and Internet Terms. 10th ed. New York, 2009. Print.