Typically an “heir” is someone who is legally entitled to inherit property from someone if that someone dies without leaving a legally valid will.
Beneficiaries are generally individuals who are designated to receive property after a person dies. They may be named in a will, a trust, or other legal documents.
Legatee and devisee are two older terms that may be encountered in legal documents involving the settlement of an estate when there is a valid will admitted to probate. A legatee is someone who is named to inherit personal property. A devisee is someone who is named to inherit real property.