This section of documentation uses the term “User Processes” to refer to the client processes that connect to an Oracle database. If you read down the page further it describes the two types of processes that run the Oracle database server code – Server Processes and Background processes. Like DCookie I have heard Server Processes referred to as User Processes, hence the confusion.
The 11.2 Concepts Guide uses much better wording (emphasis mine):
When a user runs an application such
as a Pro*C program or SQL*Plus, the
operating system creates a client
process (sometimes called a user
process) to run the user application.
The client application has Oracle
Database libraries linked into it that
provide the APIs required to
communicate with the database.
Client and Server Processes
and Server Processes Client processes
differ in important ways from the
Oracle processes interacting directly
with the instance. The Oracle
processes servicing the client process
can read from and write to the SGA,
whereas the client process cannot. A
client process can run on a host other
than the database host, whereas Oracle
processes cannot. …