The wire speed, the route is forwarded with no delay (low delay) and no loss for any input of all interfaces of the router. RFC suggests 64-bit as the shortest packet to test the throughout of the router.
E.g. one router has two 10M synchronized interfaces (one is for upstream and another is for downstream). If the throughout reaches 10M/8/64=19531pps (it handles 19531 64-bit packets every second), it can handle the packet the same as wire speed. Actually definition of wire speed in RFC is lower.
Generally the throughout of the router can be improved with the following ways: the reconstruction of routing table, the application of Cache, distributed handling, high layer switching and hardware (FPGA/ASIC) forwarding.