Fulfillment is the process of storing, packaging, and shipping ecommerce products. Shopify Fulfillment could simply mean how you fulfill items sold through your Shopify store.
However, the Shopify Fulfillment Network is a completely different service that's offered by Shopify to replace any third-party logistics you have in place.
Whenever you sell an item online it must go through this fulfillment system so that your inventory is stored properly, it has the right packaging, and your customers receive the items in a reasonable amount of time.
In addition, your method of fulfillment decides how much it'll cost your business to get those products to your customers after checkout.
Shopify fulfillment isn't much different from the general definition of fulfillment, except that it's implying that your business is being run through the Shopify platform.
Because of this, you have several integrated options that help you fulfill products on a regular basis.
