A "row" is a reference to a horizontal line on the reels of an online slot upon which the symbols appear. There are usually multiple rows on the reels of a slot, and each row can contain a different number of symbols. Winning combinations show up on lines, when certain symbols show up on a certain number of lines and in a certain order. The number of rows a game has can vary from game-to-game and affects the number of possible winning combinations. It is important for you to understand the number of rows and the order they need to come in on in order to have the best shot at winning.