A domain name can be used without a website. A domain name can be used to create email addresses, forward to other websites, social media pages, and other uses.
For example, you can use a domain name to create professional email addresses like "yourname@yourdomain.com" and forward them to your personal email address, this can give a more professional look to your emails.
You could also use a domain name to forward to other web pages such as your social media profile, or to your business's page on a different website.
Additionally, you could use a domain name for a landing page or a "coming soon" page to create a sense of anticipation for a future website, or for a parked page with your contact information.
So, you don't necessarily need a website to have a domain, but a domain name can be a valuable asset for your business, personal brand or project.