Mandolin: The soprano voice of
the mandolin family, tuned GDAE, in fifths, like a violin. During
the early 1900s, mandolin orchestras were all the rage, during
this time various instrument companies, including Gibson, Lyon
& Healy and others, manufactured instruments for these ensembles.
Mandolin, mandola, mandocello and mandobass, all tuned similarly
to their violin family relatives.
Mandola: The alto of the mandolin family. The mandola is tuned a fifth lower than mandolin, CGDA, same as tenor banjo and viola. Also sometimes called tenor mandola. Some Celtic players tune up a whole step to have mandolin fingering, DAEB. Various open tunings are possible, DADA, CGCG, DGDG.
Mandocello: This instrument is tuned one octave lower than the mandola, CGDA. It is the same range as the violoncello. It's got a big sound.
Bouzouki, octave mandolin, octave mandola: The bouzouki was first used in Celtic music in the late 1960s. The original players used Greek bouzoukis, tuned DAD for the three course instrument, GDAD or ADAD for the four course instrument. There are a number of other open tunings, also some players use GDAE, an octave below the mandolin.
Nowadays, many luthiers have been building flat-backed Irish bouzoukis or octave mandolins. It can get confusing, some manufacturers are calling long scale instruments bouzoukis and shorter scale instruments octave mandolins. Often there is no difference between them. Many players call their shorter scale instruments bouzoukis. To further confuse the issue, many luthiers make 5 course instruments called citterns, GDADA or DGDAD. We both play 4 course bouzoukis, usually tuned GDAD, and play many styles of music on it, including Celtic, Swedish, Balkan and Greek.