When you place an Object (as opposed to other elements in ARCHICAD), you are placing an instance of an external file located in an object library. ARCHICAD is shipped with a standard object library containing hundreds of preconfigured, editable objects (also known as GDL objects or Library parts). For the most part, you will use ARCHICAD tools to place objects from this standard library.
Objects are parametric. This means that you can freely configure the placed instance, using the Object Settings dialog box, or the dialog boxes associated with the object-type tools, without actually modifying the source file for the object.