In Massachusetts, a personal representative is the same as an executor. Executor is the commonly known term that was traditionally used to describe the individual appointed by the Probate Court to administer your estate after you die. Massachusetts changed the statutory name for this to Personal Representative, a more gender neutral and modern term.
If a decedent does not leave behind a Will, their estate still must be probated. Here, the court will appoint an administrator instead of an executor to serve as the personal representative to the estate. When you see that an administrator has been appointed to an estate, it indicates that the decedent died intestate (died without a Will), or their named executor(s) were not appointed by the court. Once appointed, administrators receive Letters of Administration instead of Letters Testamentary from the court.