The group or partition, over which the function operates, depending on the evaluation of the specified condition. If the condition evaluates to TRUE, a new dynamic partition is created inside the specified window partition.
RESET WHEN is optional. If there are no RESET WHEN or PARTITION BY clauses, then the entire result set, delivered by the FROM clause, constitutes a single partition.
If RESET WHEN is specified, then the ORDER BY clause must be specified also.