This is an internal name used to try to match different curves with each other. When saving and later restoring curves on a different set of curves we need a name that gives enough context to match them up by intention, and not long or short name. For example, a curve might have a short name of "X", and a long name of "Floor.Transform.Location.X". If you wanted to copy a set of transform curves and paste them onto another transform, we use this context to match the names together to ensure your Transform.X gets applied to the other Transform.X - in this example the intention is for the curve to represent a "Location.X" (so it should be pasteable on any other curve which says their context is a "Location.X" as well). This is more reliable and more flexible than relying on short display names (not enough context in the case of seeing Location.X, and Scale.X) and better than relying on long display names (too much context and no reliable way to substring them).