Context menu is a menu which is usually invisible and only appears when you click any mouse button (usually it's right mouse button), providing relevant actions to the item you clicked on.
A context menu is a menu in a graphical user interface that appears upon user interaction, such as a right mouse click or middle click mouse operation. A context menu offers a limited set of choices that are available in the current state, or context, of the operating system or application. Usually the available choices are actions related to the selected object.
Source: Wikipedia
