Since 2016 a child between 5 and 11 can be booked either at full fare with a berth or at half fare without one, and the second option shows on the PNR as NOSB. The child is a passenger on the ticket and must travel, but has no berth or seat of their own. Children under 5 travel free and do not appear on the ticket at all.
NOSB is a booking choice made at the time of reservation, not a status that changes. It cannot be upgraded to a berth after booking.
Also written or searched as: no seat berth · child without berth · child half ticket