The primary difference is that probation is an alternative to prison, while parole is essentially a shortened duration of the time spent in prison.  Probation is a criminal sentence that allows the convicted person to suspend jail or prison time in exchange for abiding to certain terms such as regular contact with a probation officer, attendance at a rehabilitation program and/or attendance at work or school.  People on probation are also subject to warrantless searches of their homes and random drug tests.  Parole is an option for completing a criminal sentence outside prison.  It is offered to a convicted felon after they have completed a certain portion of their sentence in state prison.  A person on parole will also likely have to abide to many of the same terms as the person that was sentenced to probation.