You can buy a domain name without purchasing web hosting. A domain acts as an online address with which you can refer people to a website.
Suppose you buy the domain purely to park it, for example because you think you want to use it in the future or to prevent a competitor from buying it, then you do not need web hosting. It is also possible that you already have web hosting with another party and you buy the domain from us because you are cheaper or because you want to use simple domain management. Even then you do not need an additional hosting plan.