It's a 10-String Extended Range Classical Guitar.
According to Wikipedia: "The extended-range classical guitar is a classical guitar with additional strings, normally extra bass strings past the bass E string, that are available on the fingerboard.
Many configurations have been produced, but the ten-string classical guitar received a particular boost in 1964, when Narciso Yepes performed the Concierto de Aranjuez with the Berlin Philharmonic Orchestra, using a ten-string guitar developed for him by José Ramírez III and a specific tuning designed to balance all resonances of the chromatic scale."
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