A Hybrid guitar is a bass and guitar combined into one instrument. A hybrid is typically a seven or eight string guitar on which you can simultaneously play bass lines, chords, and melodies. The bottom 3 strings are dedicated to a bass register, and the top 4-5 strings are in a guitar register, all on one neck. Each side has separate circuitry and is meant to be plugged onto its own corresponding amplifier.
A hybrid guitar is also an electric guitar with the ability to produce a signal with the tonal quality of an acoustic guitar in addition to a typical electric signal from a magnetic pickup, allowing a wide tonal pallette for performers with a varied repertoire. Hybrid guitars typically use a piezoelectric pickup to generate the acoustic-like signal, this is the same type of pickup used in most electro-acoustic guitars.
Such pickups can produce a reasonable facsimile of acoustic tone even in solid bodied instruments. Examples of solid-body hybrid guitars include the Ovation VXT,Godin A6 Ultra, and Tom Anderson Guitarworks Crowdster Plus One and Two. They are similar to silent guitars, except that the latter do not have magnetic pickups. Small-bodied hybrid guitars like the Steinberger Synapse SP2FA can double as travel guitars.
Hollow bodied hybrid guitars are also possible. Examples include the Hamer Duotone Custome (claimed to be the first hybrid guitar)Michael Kelly hybrid,Taylor T5 and, Ibanez MontageCrafter SA. These resemble semi-acoustic guitars with additional piezo pickups, The Yamaha AEX1500  is a hybrid archtop guitar.
In 1965, German-born artist and bassist Klaus Voormann invented the "Vootar," an eight-stringed guitar-bass hybrid. Vox constructed a model for Voormann, which he can be seen playing in multiple appearances with the band Manfred Mann. 
Hybrid guitars were further pioneered by guitar virtuoso Charlie Hunter.