SLD

What is an SLD (Second-Level Domain)?

The SLD (Second-Level Domain) is the portion of a domain name that appears directly to the left of the top-level domain (TLD). In "example.com," "example" is the SLD and ".com" is the TLD. The SLD is typically the customizable, brandable portion of a domain name, the part you choose when registering a domain.

Domain name structure

SLD        TLD
        ↓          ↓
    example    .  com
        │          │
        │          └── Top-Level Domain
        └── Second-Level Domain (your brand)

Full example: blog.example.com
              │      │      │
              │      │      └── TLD
              │      └── SLD
              └── Subdomain (third level)

SLD characteristics

What you can register

The SLD is the part you select during domain registration:

• Must be unique within the TLD
• Subject to availability
• Your brand identity online

Character rules

Valid SLD examples

Valid: example, my-brand, company123, x
Invalid: -example (starts with hyphen)
Invalid: example- (ends with hyphen)
Invalid: my example (contains space)

SLD types by category

Brandable SLDs

Created or invented names:

• google.com, spotify.com, airbnb.com
• High trademark potential
• Unique and memorable

Generic SLDs

Common words or phrases:

• cars.com, hotels.com, pizza.com
• Describe products/services
• High natural traffic potential

Keyword SLDs

Include relevant search terms:

• cheapflights.com, bestloans.com
• SEO considerations (diminished impact)
• Clear content indication

Geographic SLDs

Location-based names:

• newyork.com, california.com
• Local business focus
• Tourism and real estate popular

Country-code second-level domains

Some ccTLDs have additional registration levels:

example.co.uk
    │    │  │
    │    │  └── ccTLD (.uk)
    │    └── Second-level (.co = commercial)
    └── Third-level (your SLD)

example.com.au
    │    │   │
    │    │   └── ccTLD (.au)
    │    └── Second-level (.com = commercial)
    └── Third-level (your SLD)

SLD vs subdomain

Key distinction:

• SLD: Registered at registrar, appears in zone file
• Subdomain: Created in your DNS, unlimited, no registration needed

shop.example.com
  │      │
  │      └── SLD (registered, costs money)
  └── Subdomain (created free in DNS)

Choosing an SLD

Best practices

1. Keep it short: Easier to remember and type

2. Make it brandable: Unique and distinctive

3. Avoid hyphens: Look less professional

4. Check trademarks: Avoid infringement

5. Consider pronunciation: Easy to say verbally

6. Think globally: Works across languages

The SLD is your primary domain identity: the customizable component that represents your brand, business, or project on the internet.