A tooltip is a short description that is linked to another control or object. Tooltips help users understand unknown or unfamiliar objects that aren't described directly in the UI. They display automatically when the user presses and holds or hovers the mouse pointer over a control. The tooltip disappears when the user moves his or her finger or the mouse pointer. The contents of the tooltip can be text or an image but is not interactive.
Use tooltips to reveal more information about a control before asking the user to perform an action.