Instance: In object-oriented software terminology, an instance is a single example of a concrete class. The New operation creates a new object instance of the class.
In most situations, PRPC uses the term New for the act of creating a new instance, rather than the Java term constructor or instantiation. Refer PDN help of a specific PRPC version. I have referred the Pega 7.1.8 help.
Hope this answers regarding your query on instance.
An Object describes a thing. Like properties and doesn't exists. It's not in the memory of the computer. Its just a definition. When you create the object then its goes into the memory and it will exists. At that time you can access that object. An instance is the object in memory with the definition.
See it like a bleuprint of your house. The bleuprint describes that house, but you can not sleep in it.
When you build (create or instantiate) that house confom the blueprint, than you can sleep in it, or paint it
If your brother wants also a house, he uses your bleuprint to create its own.
Thanks for the reply . As you said object is a definition with no physical existence but as far as i know class provides the template and object is its physical implementation . If its correct than how object is different from instance. plz correct me if am wrong .