Definition: object references
To learn about object technology, two easy-to-read books on the subject are David Taylor's "Object-Oriented Technology: A Manager's Guide" (Addison-Wesley, 1990) and "Business Engineering with Object Technology" (Wiley, 1995). They are also excellent starter books.
For more in-depth analysis, also read "Object-Oriented Analysis and Design" by Grady Booch (Benjamin Cummings, 1994) and "Object-Oriented Modeling and Design" by James Rumbaugh, et al (Prentice-Hall, 1991).