The floating action button (FAB) is a well-known primary action button on Android devices. It is commonly placed at the bottom center or bottom right of the screen, appearing above other UI elements. Google’s Material Design guidelines recommend this placement to keep the FAB easily accessible while maintaining a clean interface.

In contrast, iOS does not have a direct FAB equivalent. Instead, primary actions are often placed in the upper right corner of the navigation bar (e.g., a "Compose" button in Mail or a "New Chat" button in Messages). Depending on the app’s design, primary actions may also appear in toolbars, action sheets, or as large buttons within the content area. Mobile developers sometimes experiment with button placement, such as integrating primary action buttons into a bottom navigation bar.