explenation for a bit less-lazy people:
dynamic recompiler recompiles (translates) machine code for the N64 (R4300 processor, RISC) into machine code for x86 (PC processors, CISC) in parts of blocks which are then executed block by block on the pc - once a block has been recompiled it doesn't have to be recompiled again - the previously recompiled block is simply executed again.
kinda minimizes ressources needed by the CPU emulation and thus is very fast (maybe twice as fast or faster?)
note: graphics and sound processing would still eat as much CPU though.....