When a person leaves a will, we say that he died testate as opposed to intestate. Blackstone defined a will as “The legal declaration of a man’s intention which he wills to be performed after his death,” a definition that maybe gives us some idea of where the legal term “will” comes from. Thomas Atkinson’s Handbook on the Law of Wills is a little more expansive and a lot more helpful (all emphasis in these quotes is mine):
A will is a person’s declaration of what is to be done after his death, which declaration is (1) revocable during his lifetime, (2) operative for no purpose until his death, and (3) applicable to the situation which exists at his death. Usually a will relates to the disposition of the maker’s property.
In other words, a will only functions after the maker, or testator, dies. Until then, the testator can change her will when she wants, willy nilly, if you will. (I’m sorry.) That is, while she’s alive, her will is revocable.
A person who receives money or property as directed by a will is called a beneficiary. Often a will names more than one beneficiary or classes of beneficiaries. For example, a testator might name her son James and daughter Julie beneficiaries, or she might simply refer to them as a class, as in “all my children, share and share alike.”
To make sure her wishes are carried out, the testator generally names an executor, the person who acts on behalf of the testator after she dies. (A quick note on terminology: If someone dies intestate {without a will}, the court appoints an “administrator.” If someone dies testate {with a will}, the will names an “executor.” Both the terms administrator and executor are included within the meaning of the term “personal representative.” Sometimes people use the terms executor and personal representative interchangeably.)