In the heading to Psalm 8, we read:
For the music director; on the Gittith. A Psalm of David.
That word, Gittith, appears also in the headings of Psalm 81 and Psalm 84.
There are two main theories about what the word means.
The first, and far more popular, theory is that it comes from the name for the Philistine city of Gath. So, a Gittith would maybe be a type of harp or lyre made in Gath. One Jewish tradition even says that it was a specific instrument that David got when he was in Gath in 1 Samuel 21.
Another theory is that the word Gittith does come from the word Gath, but in a different way. You see, the city of Gath is named from the Hebrew word Gath, which just means “winepress”. So, this theory goes that Gittith is some sort of melody associated with the grape harvest. Or maybe it’s in reference to treading on the enemies of God like a winepress.
This theory seems far less likely. However, it does have one thing going for it. In the Ancient Greek translation of the Hebrew Bible (the Septuagint), the word Gittith is translated as “winepress”. The Vulgate translates it the same way in the late fourth century.
Overall, we don’t know exactly what the word Gittith means, but the best guess thrown out is it was probably some sort of stringed instrument from the city of Gath.