Embedded components are components which have all of their definition stored within the schematic file. When a users place a component onto a schematic page, they have the option of making the component embedded. Other than storing all the symbol information inside of the schematic, an embedded component is just any other component. Embedded components are defined as:
C 18600 21500 1 0 0 EMBEDDED555-1.sym [ ... ... Embedded primitive objects ... ]
In the example above, 555-1.sym is the component. The EMBEDDED tag and the [ ] are the distinguishing characteristics of embedded components. componentname.sym must exist in one of the specified component-libraries if you want to unembed the component.