In AutoCAD, an xref, or external reference, is a reference to another, external drawing file — one outside the current drawing — that you can make act as though it's part of your drawing. Technically, a reference is simply a pointer from one file to another. The xref is the actual pointer, but many people call the combination of the pointer and the external file the xref.
In both AutoCAD and AutoCAD LT, external drawing files are just one of five different file types you can attach to your current drawing by using the Select Reference File dialog box. You use this dialog box to attach externally referenced AutoCAD drawings (xrefs), raster image files, DWF and DWFX files, PDF files, and MicroStation DGN drawing files.
Use the Attach button on the Insert tab's Reference panel to open the Select Reference File dialog box. When you attach an external drawing to your current drawing, you become the host of the external file. No need to break out the cocktails and canapés, though … it's actually your current drawing that's doing the hosting, and in AutoCAD, it's called (what else?) the host drawing. You can think of the attached xrefs as guests, but most of the time they're pretty well-behaved ones, and like the best of guests, they go away as soon as you want them to.
Xrefs have a big advantage over blocks: If a drawing is inserted as a block into another drawing, its ...