Stage piano

A stage piano is an electronic musical instrument designed for use in live performance on a stage or a studio, as well as for music recording in jazz and popular music. While stage pianos share some of the same features as digital pianos designed for home use and synthesizers, they have a number of features which set them apart. Stage pianos usually provide a smaller number of sounds (acoustic piano, electric piano, and Hammond organ), with these sounds being of higher quality, unlike regular digital pianos and home synthesizers. 
Unlike many digital pianos, which are designed for semi-permanent installation in a private home, and which have design elements which make regular transportation difficult (e.g., permanently mounted legs, modesty panel, internal power amplifier and speakers and a fixed sustain pedal), which would require a van and movers to relocate, a stage piano generally has a portable, detachable stand, no internal amp or speakers (an output jack is provided so the instrument can be plugged into a keyboard amplifier), and a detachable sustain pedal plugged into a jack. This enables a performer to remove all the detachable parts and makes it easier to transport the instrument to gigs and rehearsals.
Controls and features.
Stage pianos usually have a smaller selection of sounds than digital electronic keyboards and synthesizers. Instead of the hundreds of sounds and complex oscillator controls available on a high-end, professional synthesizer, they often have a small number of sounds, typically a variety of acoustic piano, electric piano, and Hammond organ sounds. Also, instead of scrolling through the on-screen menus used on synthesizers, stage pianos are usually controlled with simple knobs and buttons. 
Stage pianos differ from inexpensive home digital keyboards in a number of ways. Home digital keyboards provide several hundred sounds, ranging from imitation electric piano and flute sounds to buzzy synth-style sounds. However, the imitation sounds are created by relatively simple synthesis methods, rather than by sampling or complex digital signal processing-modelling, as in the case of a high-end stage piano. This means that the sound quality of presets are not suitable for a professional performance.
Stage pianos often have a heavier, more robust body, which is better able to withstand the stress of heavy touring. Unlike digital pianos designed for home use, they do not have a fixed stand or fixed sustain pedals. Instead, they are designed to be used with a separate portable stand and portable, plug-in sustain pedals. This makes stage pianos easier to transport on tours.
While almost all digital pianos and lower-end synthesizer keyboards designed for home use have small onboard powered speakers, stage pianos are often designed without onboard speakers; instead, they are designed to be used with external amplification. While small, low-powered amplified speakers may be appropriate for in-home use, they cannot provide sufficient power for on-stage monitoring in rock and jazz performance settings. While most onboard powered speakers produce between 6 and 40 watts per speaker, a typical professional keyboard amplifier will produce over 300 watts. Nevertheless, some stage pianos, such as the Yamaha P-250 or Casio Privia, do have onboard powered speakers.
Most stage pianos provide a recreation of the electro-mechanical electric pianos that were based on picking up the sound of a metal tine, reed or string hit by a hammer, such as the Fender Rhodes, Wurlitzer 200A or Yamaha CP-70/CP-80 series. Instead of using tines or strings, stage pianos reproduce sound electronically by the use of sampled or digitally modelled sounds. They usually have MIDI interfaces to permit them to be used as master keyboards, which can control other tone-generating modules, such as Hammond organ-emulators or synthesizer string modules.
Keyboards.
Most digital stage pianos have weighted keys or semi-weighted keys. The difference is how much force it will take you to push on the keys and how much the keys feel like those of an acoustic piano.
Stage pianos usually have 88 keys, which is standard for all modern acoustic pianos. However, some stage pianos have fewer keys, such as the Kurzweil SP76. It has only 76 semi-weighted keys, but is still called a stage piano because of its layout and weighted keys.
Sounds.
While the sounds or "voices" available on stage pianos is often wider than that of a digital piano designed for home use, stage pianos have far fewer voices than a typical electronic synthesizer. Stage pianos usually have a smaller selection of voices, typically acoustic piano, electric piano, Hammond organ, and a few others. Some stage pianos also provide a few basic synthesizer functions, to enable performers to play accompaniment "pads" or synth "leads."