Wholesale is different from direct-to-consumer sales, where for instance, a buyer pays up front when purchasing from your Etsy shop. With wholesale, the retailer doesn't normally pay for the goods until the time of shipment — and it may take some time for the seller to produce the goods. A seller should be prepared to float the cost of producing the goods.
Now, when a retailer asks for "terms," this refers to a type of payment plan for the retailer. For instance, a retailer may request to pay a seller 30, 60, 90 days after the invoice date — referred to as "net 30, net 60, net 90." A very common practice is net 30. Many sellers prefer to only offer terms when they feel comfortable and have a trusting relationship with a retailer. For example, the seller will ask for the first order to be paid upon shipment of goods. Then, if that first order goes smoothly, they may move the retailer to net 30 terms. Heads up that some larger retailers only operate on terms!