In the case of igoldrush.com, “igoldrush” is the Second Level Domain(SLD) or in layman terms, the part directly in front of the last dot in a domain name.
The Second Level Domain (SLD) can contain only English letters, numbers, and hyphens, except in the case of Internationalized Domain Names (IDNs) which we will address later in the guide.
In most domain names, the SLD and the TLD are the only two parts. But some countries have split their ccTLDs into multiple parts, giving industry specific organizations their own ccSLDs (Country Code Second Level Domains). For example, in 1996 .uk ceased registrations directly under .uk and users are now required to register a domain name under .co.uk (for general and commercial uses), .ltd.uk (for UK Limited companies), .me.uk (for personal websites), and so on.
Technically, in a name like igoldrush.co.uk, .uk would be the TLD, .co would be the SLD, and igoldrush would be a Third-Level Domain (there is no acronym used for this).
But for the sake of easier understanding, the online world has begun generically labeling names like .co.uk as a ccTLD all in itself, instead of splitting the names up. So, don’t get too confused if you see people (or even this site) refer to .co.uk as a ccTLD. Remember, the reason for domain names is to make it easier for people to remember things, so the simpler the language used to define things, the better.
Read on to learn more about sub-domains