A drawer is a panel that slides in from the side of a screen, while the page behind it remains nearby. It is like pulling open a desk drawer to get something without leaving the desk.
For example, selecting a product from a list might open a drawer with more details. The person can review the information and close the panel to return to the same list.
Use a drawer when the extra content is too much for a small pop-up but should stay connected to the current page. Give it a clear title and an obvious close control.