keybed

noun3

1. •
   The support structure of the key of a piano or other keyboard instrument upon which the key rests when fully depressed.

   • [T]he pressure required on the keybed to hold a note down is not necessarily more than will suffice to sound the note at its softest . . . — 1932
2. •
   The entire assembly consisting of the keys and action of a digital or electronic piano - particularly used for digital and electronic instruments in which most parts of the action are located underneath they key itself, and for which the keys, action, keystops, associated electronics, and other related parts are a single integrated assembly.

   • In recent years the term “keybed” has been used to describe the entire [electronic/digital] piano action – the keys, weights, etc. – as opposed to just the rail. — 2005
3. •
   The sturdy, flat structure of the cabinet of a piano or other keyboard instrument upon which rests the keyframe, holding all of the keys of the instrument.