When mutual funds began selling, the managers paid commission to fund brokers in the form of a load, which customers paid up front when they bought the fund. That is, they might invest $2,000 and would have paid a 5% commission so that after day one, they had lost $100 on their investment, which now showed up as $1,900 on the books. There was an additional headwind effect here in that they had a smaller base from which to compound against over time.
To mitigate the weight of this load, funds began to allow customers to defer when they paid their commissions. For some funds, it was when they redeemed. For others it was after some set period of time or when assets had reached a certain level, etc. The key idea for the 7 is that the commission in a deferred load mutual fund transaction, is paid simply "later".