A user process trace file is a trace file that is produced by user session. However, this is an optional file, which is generated if the user wants to generate the file. This file is generated when the value of SQL_TRACE parameter is set to TRUE for a session.
This parameter can be set at database, instance, or session level. If it is set at instance level, trace file will be generated for all the connected sessions. If it is set at session level, trace file will be generated only for the specified session.
The location of user process trace file is specified in the USER_DUMP_DEST parameter.
The information in user process trace file is generally used for trouble shooting.