UkuleleThe ukulele, or uke, is a fretted string instrument which is essentially a smaller, four-stringed version of the guitar.
The ukulele comes in four sizes (from smallest to largest): soprano, concert, tenor and baritone.
In the USA, soprano and concert ukes are usually tuned in the key of C: G-C-E-A from low to high, but with the G-string actually tuned an octave up, so it's pitched between the E- and A-strings. The baritone is usually tuned in G like the top four strings of a guitar, D-G-B-E. The tenor can be tuned either way, and in C tuning is sometimes tuned with the G-string an octave lower, so it's pitched below the C-string, where you might expect it.