For Defined Benefit (DB) plans, the person(s) or entity ultimately responsible for the oversight, management and administration of the pension plan, and the administration and investment of the pension fund. The Plan Administrator may delegate some or all of its responsibilities for administering the pension plan and administering and investing the pension fund to various service providers.
For Defined Contribution (DC) plans, the person(s) or entity identified in the Plan Document as having responsibility for the oversight, management and administration of the DC Plan. It could be the employer, a committee of employees, a company executive or someone hired for that purpose. The Plan Administrator may delegate some or all of its responsibilities to various service providers.