what is the means of polyphony.
if a keyboard has more notes of polyphony than the other one, does it mean that its sounds are better than the other one?

what about internal wave rom?

polyphony=the maximum number of notes that can be played simultaneously. It can get complicated, but I believe this is the simplest explanation: If you had a keyb with 32 notes polyphony AND you had 32 fingers and all of your 32 fingers pressing the keys at the same time, you would be able to hear all the different notes.
polyphony does not mean better sounds, means more sounds heard at he same time.
wave rom=the bucket where sounds (waves) are located inside the keyb, Wave (R)ead (O)nly (M)emory

The subject of polyphony is particularly important for arranger and/or midi file users because each note used by the arranger keyboard for drums, bass and style instruments counts against your polyphony. Furthermore, some instrument companies, like Yamaha, layer their sounds to make them sound better... so for example, holding down five notes with one hand could easily equal ten or more notes of polyphony. Also, every company has their own voice allocation scheme (how the polyphony is distributed when you run out of notes) and some are better than others at hiding their polyphony limitations. Suffice to say that more polyphony is usually better.

Most newer arranger keyboards are going with a standard 128 notes of polyphony, although some are less (Korg PA1X: 62 notes) and some are expandable (Yamaha 9000 Pro). Some home keyboards like the Yamaha CVP-900 have 256 notes of polyphony with 128 dedicated to backing/styles and 128 dedicated to the piano.

Perfect explainations.