Customer leads are any shopper that has not ordered from you yet but have either abandoned a cart or Watch your store. Send them a discount and cart abandon message to get them to place their first order.
Customers are any shopper that has placed an order with your store. Send them a discount code as a thank you to incentive them to purchase again and again!
Repeat Customers are any shoppers that have placed more than one order with your store. These are your best customer. Send them a discount code for being so awesome!