This reports the count of adjacencies whose Layer 2 encapsulation header may need to be updated, fixed up, at the actual moment of packet switching, rather than having a fully static encapsulation precomputed. This matters specifically for tunnel-type adjacencies, like GRE or IP-in-IP, where part of the outer header, such as an IP header with a variable length or checksum, cannot be precomputed and must be filled in per-packet, so a high count here indicates significant reliance on tunneling that carries a small per-packet CPU cost compared to static-encapsulation adjacencies. A router terminating dozens of GRE tunnels would show a correspondingly higher count here than a router with mostly directly-connected Ethernet adjacencies, reflecting the extra per-packet header-fixup work those tunnel adjacencies require.