Repeat orders can mean two things in ecommerce: when a product gets reordered by the same customers or when a customer just places another order. Both are signs of high customer satisfaction and good customer retention.
If you monitor product performance, you should be able to see both unique and repeat orders of each product (if applicable to your kind of products, of course). This will tell you how much those products are liked and satisfactory.
On the other hand, a repeat order by a customer, with no regard to the products ordered, shows customer loyalty. People with most repeat orders are your VIP customers.