Funds that don't pay a fee to the online brokerage but allow the brokerage to impose transaction fees to cover its costs. However, there are no sales commissions to pay in purchasing these funds. But since you're buying it from a different online brokerage you'll pay a transaction fee. Obviously, it may pay to shop around and see if you can buy the fund direct or, perhaps, through another online brokerage that charges a lower fee. Trading funds within the same family is called an exchange.
Loads are generally a percentage of the purchase price.
Again, not all funds are listed on the brokerage sites. Transaction fees for buying and selling non-NTF load funds and for exchanging within the same family vary widely. Make sure you see fees in writing before investing. A few of the brokerages have an extensive network of walk-in branches. Generally, if you have an online account, the most you can do at the branch is drop off checks and securities rather than mailing them.