When a performer (e.g. a guitar player) performs a solo in a recording, in MusicBrainz that can be indicated by checking ‘solo’ for that artist/instrument role.
In MusicBrainz it will then show up as the artist performing ‘solo guitar’.
To me that looks funny, suggesting that ‘solo guitar’ is some instrument.
(or, you could have a composition for ‘solo guitar’, but that’s not what’s meant here)
Wouldn’t it be better if it displayed as something like: ‘guitar (solo)’?