Probation and parole are sometimes used interchangeably though they are distinctly different. When a court places someone on probation it means that, instead of the individual being incarcerated, they will instead be supervised in the community, typically by a probation officer.
There are different levels of supervision that can apply to a probationer based on what the court sentences them to. Active supervision means that the probationer must actively and on a regular basis check in and report to a probation officer. The reporting can be required to be done either in person, by mail or by phone on a predetermined schedule. Failure to do so could result in a probation violation.
If no active reporting is required by the court then the probationer is said to be on an inactive status. Whether a probationer is placed on an inactive status or not is usually dependent on the severity of the offense for which they have been sentenced.
Often times the court will impose conditions which need to be met while a person is on probation. For instance, one can be required to pay certain fines or fees that they may owe to certain institutions or individuals. Sometimes one may be required to complete a treatment program like drug rehabilitation. Typically, if one does not meet the conditions of their probation often times one risks being incarcerated on a probation violation.
Parole, on the other hand, means that a criminal offender has met certain conditions while they were incarcerated that allows them to be released back into the community to serve out the remainder of their sentence. Once parole has been granted, the parolee has the same supervisory rules that apply to probationers. They may be placed on an active status with regular check ins, or inactive status. Also, just like a probationer, the parolee may also have conditions tied to the terms of their parole. If the terms aren't met then the parolee almost always risks getting their parole revoked and become incarcerated once again.
Source: Office of Justice Programs, "What is the difference between probation and parole?," Accessed Jan. 12, 2015