Source:
http://en.wikipedia.org/wiki/zither.htm
The zither may be regarded as a harp with a very large soundbox. The strings are strung across the soundboard. It is typically played on the lap of the musician, or on a table. The name zither might be a variation of the Greek kithara, and dates back perhaps to as far as 600 BCE.
The zither has a combination of "open" strings and strings on a fretboard. The strings are plucked.
Source:
http://en.wikipedia.org/wiki/zither.htm
http://en.wikipedia.org/wiki/Zither