A context menu provides the user with instant actions. It can be filled with text commands. Context menus can be light dismissed by tapping or clicking somewhere outside the menu.
Dialogs are modal UI overlays that provide contextual app information. Dialogs block interactions with the app window until being explicitly dismissed. They often request some kind of action from the user.
A flyout is a lightweight contextual popup that displays UI related to what the user is doing. It includes placement and sizing logic, and can be used to reveal a hidden control, show more detail about an item, or ask the user to confirm an action. Flyouts can be light dismissed by tapping or clicking somewhere outside the popup.