Touch Sensitive.This simply means that volume of sound can be increased by increasing finger pressure on any one of the instruments keys.
GH (Graded Hammer Action)
Real acoustic pianos have a mechanical action. To simulate the mechanical feel of this action digital piano manufactures have developed the Graded Hammer Action. There is however a great variation in the feel and touch response of GHA's. Lower price instruments will have a 'basic' GHA, whilst more expensive instruments will give a key touch that more closely resembles that of a real piano.
Polophony Early keyboards and synthesizers were made ‘Monophonic’. With a monophonic instrument, musicians had to play one key at a time. A key was then depressed and it had to be released before a second key was played. Over the years technology improved and keyboards were made ‘polyphonic’, so that 2 or 3 or more keys could be played together. Today’s digital pianos have a polyphonic capability of 64 to 128 notes/keys !
Digital Sound SamplingTo obtain a piano sound that is similar to a true acoustic sound, manufactures record a piano tone on to a micro chip. This chip / tone generator then releases the sound when the instruments key is depressed.
Tone is made up of pure Tone and Noise. On any instrument, including Digital Pianos, the percentage of Tone to Background Noise will vary from one model to another. There is a certainty though, and that is : The use of low quality materials will increase THD ( total harmonic distortion / background noise ) High levels of THD can lesson the enjoyment of playing piano
Wattage is simply the power of the instrument. This usually relates to the instruments volume of tone. However high Wattage does not necessarily mean a better quality sound ! For that please see THD