A domain suffix, also known as a top-level domain (TLD), is the last part of a domain name, such as .com, .org, .net, or .edu. These suffixes help categorize the domain based on its purpose or origin, with .com typically used for commercial entities, .org for organizations, and .edu for educational institutions. The domain suffix is not the beginning of the web address or a security feature but rather the final part of the domain name.