External References also called as xrefs in AutoCAD, allow you to view any drawing as a reference in your current drawing. The Referenced drawing will be treated as an external drawing and will not be the part of your current drawing. External References gives you the flexibility of laying one drawing on top of another in any location, scale and rotate and being able to see both at the same time.
When you attach a drawing as an xref, you link that referenced drawing to the current drawing; any changes to the referenced drawing are displayed in the current drawing when it is opened or reloaded.
