Emulation
Beginner
Running a chip design on a big, special machine. It is fast enough to start real software, but slower than the finished chip.
Novice
Running the design on a dedicated machine, built from many FPGAs or from arrays of custom processors, that executes it in hardware at up to a few million clock cycles per second. That is fast enough to boot an operating system before the chip exists.
Expert
Trades compile time, visibility and price against speed. Processor-based emulators compile quickly and can record every signal; FPGA-based ones compile slowly and need a recompile to watch different signals. Everything mapped onto the machine must be synthesizable.
Explained in Verification (Design Flow).
See also: FPGA prototyping, Simulation (logic simulation).