Mutual fund shares purchased by individual investors as opposed to institutional shareholders. In general, the amount invested in the fund is what distinguishes investors from institutional shareholders. In many cases, a fund will have a minimum investment that must be made to qualify as an institutional shareholder.

For example, Vanguard has a shareholder category called Admiral Shares, which requires a minimal investment level of $100,000 in a fund. At this level, a fund shareholder will benefit from a slightly lower expense ratio as well as certain service benefits.

If a fund carries a load, it will apply to investor shares, whereas institutional shareholders will generally have this fee reduced or waived completely because of the size of their investment.