This counts accounting requests to this server that got no response at all within the retry window. Per the shared description text, a timeout that triggers a same-server retry also bumps Retransmissions, and one that triggers a send to a different accounting server also bumps that server's own Requests counter, so a single lost accounting record can be traced across several counters and even across table rows. For example, a single dropped stop-record for one session could register as +1 here, +1 on Retransmissions if retried to the same server, or +1 on a backup accounting server's Requests if the switch failed over, all stemming from one accounting event.