The part where the neck and and body of a ukulele are joint. Its position is relevant for the playability of the instrument: From this position on, the body interfers with the higher frets, making it difficult to play bar chords. However, this problem of design (actually only relevant for Ukuleles bigger in size than sopranos) can be evaded with a cutaway.

The sound at the neck joint of an acoustic Ukulele is mellow and bright and corresponds to the register sul tasto.

Typical Ukukele neck joints