An Item Discount gives your client a discount based on a certain item in their cart. Some examples of Item Discounts are: "Buy three 5x7s for $5 each" or "Choose three 8x10s for free" or "Buy ten 4x6s and get 20% off of each".
Item discounts can be Automatic, or Promo Code based. Automatic discounts apply to all eligible items in a cart automatically, while Promo Code discounts require that the client enter a Promo Code in the cart or at checkout in order to receive the discount.