Tooltips: Tooltips are floating labels to describe or add additional information when users hover over, focus on, or click an interactive element. Usually 3 words or less.
Popovers: A popover displays rich content in a non-modal dialog to describe or add additional information when users hover over, focus on, or click an interactive element. User can interact with popover content, including selecting text or clicking links.
Modals: Modals show additional content in a layer above the page with an overlay covering the page behind. Use sparingly.
Here are some examples of existing design systems: