The distillate created from the leaves of the hazelnut-bush-like-magic-tree commonly called Witch Hazel. The distillate from the leaves is probably the gentlest, most diluted version of any kind of With Hazel ingredient.
The leaves contain much, much less active components than the bark (4.77% vs 0.04% tannins) and distillates are more diluted than extracts. So this one is probably just a "fancy-water" that resembles the properties of Witch Hazel Extract (astringent, soothing, antioxidant, antibacterial) in a very mild and gentle way.
We have gone into much more details about Witch Hazel here.