This OID counts, in seconds, how many receive-side one-second intervals on this WAN 10G SONET (WAN-PHY) interface were severely errored, exceeding the higher error-rate threshold that distinguishes a severely errored second from an ordinary errored second. This RX-side severely-errored-seconds count is one of the standard metrics used to judge whether a SONET/SDH circuit is meeting its availability commitments, since these intervals typically correspond to visibly disrupted service. For example, a jump in severely errored seconds on a 10G WAN-PHY interface carrying SONET-framed Ethernet across a long-haul span during a specific hour would let an operator correlate the circuit problem with other events logged in that same window, such as a power event at a regeneration site.