Tooltips are text labels that appear when the user hovers over, focuses on, or touches an element on the screen. Can be used to provide information of concepts/terms/actions that are not self explanatory or well known. Can be introduced to provide information of a disabled actionable element, e.g. for disabled buttons provide information why why they are disabled.
Avoid using tooltips to provide instructions or guidance. They shouldn't be used to show rich information including images and formatted text and avoid placing over plain text or other places where they are not discoverable.