Massachusetts Attorney Thomas Swain Smith explains the difference between Probate and Nonprobate Property:
Your Last Will and Testament controls the disposition of your probate property, only, and if you die without a will, known as dying intestate, the intestacy statute only controls the disposition of your probate property.
Non-probate assets have their own mechanisms of changing legal title after the death of the owner.
Non-probate assets include any property held in joint tenancy or tenancy by the entirety with right of survivorship, property titled in the name of a Revocable Living Trust, IRA accounts, or life insurance proceeds.