Both probation and parole represent ways for people convicted of crimes to avoid doing time. What's more, they're both conditioned on good behavior -- if the offender messes up, they're shown back to their cell. But there is a major procedural difference between probation and parole. Probation is part and parcel of the offender's initial sentence, whereas parole comes much later, allowing the offender early release from a prison sentence.
Probation is handed down by the judge at trial. It may be in lieu of jail time or in combination with some jail time. The judge will specify restrictions on the offender's activities during the probationary period.
Parole is granted by a parole board, after the offender has served some -- or perhaps a lot of -- time. The parole board may consider factors such as the offender's behavior in prison and level of rehabilitation, and let him or her out early. The parole board can also specify restrictions on the person's activities while on parole.
Last but not least, probation has one more vowel and two more consonants than parole.