C is a key concept in index funds, which represents the income model of funds. In some index funds, C stands for passive management, that is, the fund manager will try to track the changes of the index to obtain income. This is different from actively managed funds, which are fund managers who actively choose stocks and trading opportunities. C does not mean that all index funds are passively managed, or that some index funds gain income through active management.

C has another possible meaning in index funds, representing the category of funds. For example, in ETF, C usually represents the category of dividend reinvestment. In this kind of fund, the dividends obtained by the fund are reinvested in stocks to increase the value of the fund. This way makes the fund's rate of return higher, but investors also need to bear certain risks.

For investors, the significance of C lies not only in the way or category of fund income it represents, but also in its influence on fund expenses. In passively managed index funds, the lower the C, the lower the management fee of the fund. Similarly, in ETFs, the fund fees for dividend reinvestment are generally low. Therefore, investors need to choose a Class C fund that suits their risk preferences and expected returns, and fully understand and evaluate the fund fees.