Greek long necked lute related to the Turkish Saz; 3 or 4 double courses of metal strings. Adopted by Irish musicians more recently.
The Bouzouki is a long-necked Lute developed in Greece from its Turkish roots. Originally 6 stringed, it now usually has 8 strings tuned CFAD. It was picked up by Irish musicians travelling abroad and adapted for their use by retuning to GDAE or GDAD. Modern makers then started producing them with flat backs which made them almost identical to the octave mandola. The crucial difference is the scale length, which is longer. This can affect fingering, but also affects sound because the strings are thinner. Generally the mandolas are better at tunes, bouzoukis for accompanying, but this is not a strict rule.
The ‘Irish’ Bouzouki has a brighter more open sound, and is easier to hold. The scale length is now generally a little shorter than Greek bouzoukis, and the distinction between Bouzouki and Octave Mandola (also known in America as Octave Mandolin) has become blurred, as the neck length is the only difference. We describe instruments with a scale longer than around 580mm as Bouzoukis. Tuning is usually either GDAE, or GDAD.
Roundback Greek bouzoukis have a longer scale length around 670mm, and are usually tuned to CFAD. Many flat back “Irish style” bouzoukis have a shorter neck, from around 610mm upwards, though they do also come with the full 670mm neck. String gauges need to be chosen to suit the neck length and tuning.
The Bouzouki is a long-necked Lute developed in Greece from its Turkish roots. It comes from a different branch of the lute family than the mandolas do. It was originally a 6 string instrument (DAD) but more modern Greek makers started making an 8 string bouzouki tuned CFAD, one tone below the top four of a guitar. The original Greek style bouzoukis are still very popular, both for Greek music, and accompanying traditional folk music.