A domain is the URL, or the website address, where your customers go to find your store online. You manage your domain settings for your online store on the Domains page in your Shopify admin. If you use the wholesale channel, then you manage the domain settings for your wholesale store on the Domains page in that channel.
By default, your primary domain is in the form of examplestore.myshopify.com, but you can buy a different custom domain or use a custom domain that you already own.