An investment fund that has investment holdings in both public and private equity. This is to say that it invests in companies that are traded publicly, and in companies that are privately held.
To find out if a fund is a crossover fund, simply look at the general investments that it makes, either by examining its holdings, or by looking at the fund's prospectus. If you realize the fund does hold both public and private equity, then that particular fund is indeed a crossover fund.
These funds are typically high yield/high growth funds.