Sue Conger's "The New Software Engineering"
Read the "Definition of Object-Oriented Terms" section in Chapter 11 (pages 461-463). This section will cover basic object-oriented terms including classes/objects, abstract data type (ADT)/encapsulation, whole/part and generalization/specification classes, inheritance/polymorphism, and messages. Take your time in reading and jot down any ideas or notes that stand out to you as particularly useful (or, conversely, confusing).
Click The New Software Engineering.pdf link to view the file.