A Hash Code is like a signature. It is used to (almost) uniquely identify objects, based on their value. Say you have two Strings, A="Hello" and B="World". Both A and B are of type String, but they will produce a different hash code because their value is different.
Why do we need hash codes? The short answer is that we need them so that objects can be used in Maps. Objects are stored in different places in Maps depending on their hash code. We say that objects "hash" to certain locations in Maps. Hence the term "HashMap"! [ October 13, 2004: Message edited by: Fletcher Estes ]