Probation is the suspension of a jail sentence - the person who is "on probation" has been convicted of a crime, but instead of serving jail time, has been found by the Court to be amenable to probation and will be returned to the community for a period in which they will have to abide to certain conditions set forth by the Court under the supervision of a probation officer. General conditions may include maintaining employment, abiding to a curfew, living where directed, abstaining from unlawful behavior, following the probation officer's orders and not absconding.
Usually the offender is supervised by a probation officer, to monitor their performance during the probation period. The probation officer helps the offender to adapt to living in the community; to guide and help them to behave in a lawful and responsible way.