Once the first chart is prepared, any berths that remain unallotted, including those released from unused quotas, become current availability. They show as CURR_AVBL in the availability table and can be booked at normal fare, without a waitlist, until the final chart shortly before departure.
It is the last legitimate way to get a confirmed berth on a train that showed a waitlist all week, and worth checking in the hours after the first chart is out.
Also written or searched as: current availability · current booking · CURR AVBL