Overlays & Surfaces · Menus
Flyout
also known as flyout menu, cascading menu, submenu
A flyout is a menu or lightweight panel that expands horizontally to the side, often as a submenu that appears when hovering an item that has children. It creates cascading, multi-level navigation. Microsoft also uses 'flyout' broadly for small contextual surfaces (menus, pickers) that appear near a control.
See it live — shadcn/ui · MUI · Ant Design
Don't confuse it with
A flyout opens to the side (often as a cascading submenu), while a dropdown opens downward. In Microsoft's terminology a flyout can also mean a small popover-like surface, so the word overlaps with popover when it holds non-menu content.
In the wild
Hovering a top nav item on a store site that reveals subcategories to the right shows a flyout.