A context menu is a menu with element-specific commands for the currently displayed element. Typical commands are:
"Update" - the currently displayed content is updated.
"Edit" - another view is displayed, in which the properties of the currently displayed element can be edited.
"Display log" - the log for the element is displayed.
"Delete" - a delete dialog is displayed for the element (although the actual deletion occurs after the corresponding answer to a security query).
Depending on the element and command, appropriate rights are required in order to be allowed to execute the command. See User Groups.
These context menus have nothing to do with the browser context menus reached via right click.