Oracle Instance Concepts - Oracle 10g Database Administration Concepts and Implementation Made Simple - page 94

Figure 4-1: The complete Oracle system i.e. Oracle Instance and Oracle
database. The background processes and memory architecture
constitute the Oracle Instance.
The thing I want you to memorize if you haven't memorize it
yet, the definition of Oracle Instance i.e. the background
processes and memory architecture constitute the Oracle
Instance.
Oracle Instance can be defined as, the background processes and
memory architecture constitute the instance. There are very few
things in this whole topic that I will request you to memorize and
this definition is one of them. Now the question is what is a
“background process”? And what is “memory architecture”? To
better understand these two things I want to give you the analogy
of the way human brain. Human brains works pretty much the
same way Oracle Instance works.