A 'development' store is essentially a new Shopify store/account which is in a perpetual trial period. It allows us to setup a large portion of the site, at our own speed (no time limitations), and without being charged Shopify's monthly fee. It's worth noting that development stores cannot process sales (or else folks would just use development stores, and wouldn't have to ever pay monthly fees). Any development store can be instantly turned into a regular paid store, by selecting a monthly Shopify plan.