When someone passes away, their affairs (i.e., their estate) must be settled (assets collected, debts paid off, distributions made, etc.). Depending on a variety of factors, the person responsible for settling these affairs may be known as a personal representative, administrator, trustee, etc.
An executor and a trustee are distinct roles involved in the management and distribution of assets in the context of an individual's estate, although it is not unusual for the same person to be named to both roles.