The happy little Hawaiian stringed instrument that looks like a small guitar is a ukulele. Most ukuleles have four strings and are light enough to be strummed by anyone, including kids.
The ukulele, or uke, as it's frequently called for short, comes in four standard sizes: soprano, concert, tenor, and baritone, and even more less-common variations. The larger the uke, the deeper and louder its sound. Some ukuleles are even double-strung, with a total of eight strings. A good ukulele player's fingers move extremely fast, which explains its name, which means "leaping flea" in Hawaiian.