When using daily fantasy sports (DFS) sites, users are required to pay an entry fee called a "rake." This fee does not count toward the bet a player is placing; it simply allows them to start betting.
The rake ensures that the site can make money in order to keep advertising and attracting players. This, in turn, ensures that there will be enough players to keep competition steady.
Rakes exist in many online gambling arenas, most prominently online poker. Online poker sites award "rakebacks" to their players, which are redistributions of rakes, usually as a percentage of the original rake. These incentivize users to keep playing and are usually given as some sort of site credit.
Fantasy sites, however, do not give traditional rakebacks. They do offer discounts and distributions in the form of bonuses and promotional codes, but they are technically not rakeback money.