Setting a field control's Display Only property to true makes the control uneditable.
You can still show the field control on the page, which will display the field's current value as text.
Note that Display Only is a property of the field control, and not the field itself. You can add multiple field controls to a form for the same field, some of which might be editable, and others display only. This is useful for have a user input filed on one page, and then showing the value they entered on a later page as uneditable text.