The context menu of an element is the menu that appears when you make a right click with the mouse button on the element. This element can be a visual object (button, icon), a record of a table, a row of a list, a word in a text, etc.
If your mouse is set up for a left-hand use, the right-click button will be the left one.
Make a right click on a working paper. You will open a context menu that gives access to numerous actions, such as editing, entering comments and tickmarks, etc.