The term "grid" is made in referrence to the arrangement of symbols on the reels of a slot. A grid can consist of three or more rows and columns, and it defines the number of symbols that appear on the reels for each spin. Each symbol has its own value and can lead to a win if it shows up in a winning combination. The size and number of rows and columns on the grid varies from slot to slot, and affects both the number of ways in which you can win and the house advantage (so-called house edge).