The banker could be both the dealer or the player, but both scenarios entail the same outcome. In the gambling terminology, the banker is the person who other players bet against at the table, and this role usually switches between people on every turn. This term is mostly used in baccarat.
For example, in some casinos, players will switch in the role of a banker every few baccarat hands. This gives everyone a chance to play as a banker and as a player and test their skills and luck in both roles.