Wiktionary
n. (context musical instruments English) A type of lightweight piano which reproduces the sound of a standard piano by electronic means. The keys are designed to feel like the keys of a real piano, and many are built to resemble one also.
Wikipedia
A digital piano (not to be confused with electric piano and electronic piano), also known as piano synthesizer, portable piano, weighted keyboard, or in the late 1980s, personal electronic piano, is a modern electronic musical instrument; a variation of electronic keyboard or synthesizer designed to serve primarily as an alternative to the traditional acoustic piano, both in the way it feels to play and in the sound produced. It is intended to provide an accurate simulation of an acoustic piano. Some digital pianos are also designed to look like an acoustic piano, both the upright or grand piano body style. Digital pianos use either an electronic synthesized emulation of the piano sound or a sampled piano sound, which is then amplified through an internal loudspeaker. Digital pianos typically have weighted or semi-weighted keyboards, which attempt to recreate the feel of an acoustic piano.
While digital pianos may sometimes fall short of a real piano in feel and sound, they nevertheless have other advantages over acoustic pianos. Digital pianos cost much less than an acoustic piano and most models are much smaller and lighter in weight than an acoustic piano. As well, digital pianos do not need to be tuned, and their tuning can be modified to match the tuning of another instrument (e.g., a pipe organ). Since digital pianos produce their sound electronically, the volume can be made louder or softer using a volume control. Digital pianos can be connected to a keyboard amplifier or PA system to produce a sound loud enough for a large venue. At the same time, most digital pianos can be played using headphones, which means that they are quiet enough for practicing in an apartment or hotel room. Some digital pianos can also emulate other sounds besides the piano, the most common ones being pipe organ, electric piano, Hammond organ and harpsichord. Digital pianos are often used in school and amateur performances to replace traditional instruments.