Your financial year is divided into periods — usually its months, each with its dates and its year. Every posting names a period, and a period has two states: open and closed.
Closing a period (from the Periods list, behind the post periods permission, with a confirmation) blocks every further
posting into it — module documents, journals, auto-post, all of it.
It is the month-end discipline that lets a reported month stay
reported. If goods received but not invoiced have aged past your
company's warning threshold, the close tells you — naming the items
and their total — and then lets you choose: it warns, never
blocks, because chasing a supplier's invoice should not hold the
whole month hostage. The warning itself is recorded on the period's
timeline. The close also reports any proposed standard costs
still waiting for activation (§6.8) and when standards were last
activated — activation is a period-boundary act, so if the waiting
proposals belong in the month you are closing, activate them first
and close after.
Reopening (the same permission) lifts the block when a closed month genuinely needs a correction — which then travels as a reversal or a new document, as always (1.6), never as an edit. Treat reopening as the exception it is: the fact of it stays on the record.