A valid domain name meets the following requirements:
- A domain name contains only letters, digits, and hyphens (-) and cannot start or end with a hyphen.
- A domain name cannot start or end with a hyphen.
- A domain name label cannot exceed 63 characters.
- Every two labels are separated using a dot (.), and the total length of a domain name, including the dot added at the end by default, cannot exceed 254 characters.
For example, example.com and www.example.com are valid domain names.