Tahitian ukuleles are very different from the standard Hawaiian ukulele. They are solid bodied, and have eight strings (in pairs). They tuned to the same notes as the ukulele (Gc C, E and A) but the C and E strings are an octave higher than the uke.
They are often intricately carved: dolphins and turtles seem to be popular themes. They have a much sharper tone than standard ukuleles (closer to a banjolele). The sound of them is probably most recognisable from the Arrested Development theme tune.
The Sunshiners from Vanuatu perform AC/DC's Back In Black on Tahitian ukulele.