Oracle Scheduler - Oracle 10g/11g Data and Database Management Utilities - page 193

Program : Program and Job are two different concepts. Program relates to the
metadata about what should be run; it specifies the program object, the program
action, and the program type. A Job specifies when the program is to be executed,
so the same program can be scheduled at different times and frequencies by different
jobs. When working with programs, the program is meant to separate the what part
of the job.
Schedule : The Schedule defines the point in time when a job is programmed to be
executed, and how often the job will be executed (frequency). This could be just a
onetime execution or a repetitive execution. For jobs to be scheduled at a later time,
it specifies when the job will start executing, and for repetitive jobs it also specifies
the start time and whether the job will run indefinitely or when the job schedule will
expire. The schedule also specifies if a job will be executed when an event is raised. A
schedule is also a database object. When working with simple jobs, the job can define
what is going to be run and when it is going to be run. The Schedule is a means of
separating the when part of the job.
Job : A Job is a user-defined task programmed to be run at a specific point in time, a
job specifies what will be run and when it will be run. This task may be programmed
to be run once or several times. The task could be a PL/SQL block. A job is a
database object.
Job Classes : If you create several jobs that share the same attribute values, then those
jobs could be included under the same job class. If a Job is assigned to a Job Class
then the job inherits the attributes defined for that Job Class. All the jobs belong to
a job class, if a job class is not specified at job creation time; the job automatically
belongs to the DEFAULT_JOB_CLASS .
Window : A Window is a time frame used to redefine allocation resources among
jobs. The Window is defined along with resource manager to specify resource
allocation policies. The Window specifies the resource plan to be activated and
each job class specifies which resource consumer group to map. The Windows may
overlap in time, if this happens the Window with the higher priority is chosen over
the Window with lower priority.