In this subtitle the following words have the meanings indicated. “Fiduciary” means: a member of the Board of Trustees; a member of the Investment Committee; a member of a committee established by the Board of Trustees as authorized under § 21–108 of this title; a member of a committee established under § 21–122(g) of this title; or an employee of the State Retirement Agency who exercises any discretionary authority or control over: the management or administration of the several systems; or the management or disposition of the assets of the several systems. “Several systems” includes the optional retirement program to the extent that the Board of Trustees administers the program under Title 30 of this article.