A tooltip shows additional information, tips, or hints related to a specific piece of UI.
Use tooltips on interactive items that show no display text, for instance, a button with only an icon. The tooltip should inform the user of exactly what action will happen if the item is activated — avoid overly vague descriptions. For example instead of "Edit", the tooltip should read "Edit application".
Tooltips are activated when the element/icon is hovered or focused upon. Tooltips should not not include actions or links.