The person who provides the property is the disponer, and the disposition is the method by which the property passes.
Where property passes by will, the disponer is the testator. Where property passes on intestacy (no will), the disponer is the deceased.
The term disposition is widely defined to include not only a will or intestacy, but any method (including any trust covenant, agreement or arrangement) by which property can pass.
The date of the disposition is the date of death of the disponer in the case of property passing by will or intestacy, and in other cases it is the date on which the disponer provided the property (or bound himself to provide it).