What are additional divisions under a second-level domain known as?

The term for additional divisions under a second-level domain is "subdomains." A subdomain is a subset of the primary domain that helps to organize and navigate to different sections of a website or server. For example, if you have a second-level domain like "example.com," you could create a subdomain like "blog.example.com" or "shop.example.com" to differentiate specific areas of your site.

Subdomains play a crucial role in web structuring as they can be used for various purposes such as hosting separate content, running different applications, or creating divisions for different user groups, all while being part of the overarching domain.

The other options do not accurately represent this concept. Domains refer broadly to the entire internet naming structure, hosts indicate specific devices connected to a network, and top-level domains (TLDs) like .com, .org, or .net exist at the highest level in the domain hierarchy, above second-level domains. Thus, understanding subdomains is essential for organizing web resources effectively.