Which of the following is a condition under which a probation officer may modify probation terms?

A probation officer may modify probation terms primarily when a violation is observed. This condition is significant because monitoring and enforcing compliance with probation conditions is a core responsibility of a probation officer. When a probationer fails to adhere to the established terms, such as failing drug tests, missing appointments, or committing new offenses, the probation officer has the authority to address these violations. Modifying probation terms in response to violations allows for a necessary adjustment in the supervision level or requirements placed on the probationer, which can help promote accountability and rehabilitation.

While the other conditions mentioned—routine meetings, the court’s session, or a probationer's request—may offer opportunities to discuss or review probation terms, none provide the same immediate basis for modification as a violation. Routine meetings are primarily for monitoring progress rather than initiating changes, and while a court session might lead to changes under judicial authority, it is not the direct purview of a probation officer. A probationer's request may be considered, but it is typically contingent upon their behavior and any observed violations, underscoring why a violation is the primary facilitator of adjustments in probation terms.