What is this instrument called?
The musical instrument in the picture is called a mandolin. It belongs to the lute family of instruments and has a variable number of strings. It looks a lot like a guitar: this instrument with half-pear-shaped body and a fretted neck. The techniques are also similar to guitar finger picking techniques. The mandolin is also often plucked with a plectrum. The first instrument of this kind was developed from the mandola, a lute from the 17th century. It had 5 double strings. The usual modern mandolin (also widely known as the Neapolitan mandolin) has 4 pairs of strings and is a bit smaller that the original. Notable uses of the mandolin in serious music are in Mozart's Don Giovanni and in pieces by Beethoven and Mahler.
There are many styles of mandolin, but three are common, the Neapolitan or round-backed mandolin, the carved-top mandolin (shown here) and the flat-backed mandolin. The round-back has a deep bottom, constructed of strips of wood, glued together into a bowl. The carved-top or arch-top mandolin has a much shallower, arched back, and an arched top—both carved out of wood. The flat-backed mandolin uses thin sheets of wood for the body, braced on the inside for strength in a similar manner to a guitar.
More Info:
en.wikipedia.org