Guest Erin, a mandocello is basically a bigger, lower-pitched mandolin. Back in the early 20th century, Gibson started manufacturing mandolin-family instruments that corresponded to the instruments in the violin family. There was the mandolin (tuned the same as a violin), the mandola (tuned like a viola), the mandocello (cello) and the mandobass (double bass). They had mandolin orchestras and ensembles, which they promoted in large and small communities across the USA. The trend kind of died eventually, but you can still find these instruments -- old ones, and modern versions -- and you sometimes hear them used in Celtic-influenced music these days. Tim O'Brien is one well-known musician who plays the mandocello quite often (his is built in the shape of a guitar, but if you look closely you can count eight strings arranged in four pairs).