1.NounA (usually large) organization that invests (usually large amounts of) money, often on behalf of others for whom it is a fiduciary (such as workers building their savings toward their retirement).
"The state employees' pension fund is the main institutional investor with a stake in that company."
2.NounAny of the individual persons whose money is invested by such an organization.
"This level of risk does not appeal to institutional investors who are worried about a nosedive of their 401(k) balances."