In the Domain Name System (DNS), Second Level Domains (SLDs sit below Top Level Domains (TLDs) in terms of the hierarchical order. They appear in the address directly to the left of the TLD, so in the domain name nominet.org.uk, .org.uk is the SLD. Second level domains are commonly used to indicate the type of organisations that the domains belong to. For example, the SLD .org.uk is mainly used by organisations and not-for-profit companies, .co.uk is used by companies and businesses and .me.uk tends to be reserved for personal use.

We run two type of SLD under .uk: those that we manage directly and those where we delegate the management to other organisations.

The second level domains we manage are:

co.uk

A fully open domain, this is the largest SLD in the UK and is intended for use by commercial enterprises.

ltd.uk

This is a restricted SLD available only to registrants that are able to pass a test as outlined in the Rules for the Registration and Use of Domain Names. The restrictions are designed to work with the system used by Companies House, so companies should always be able to have a domain name which closely matches their company name and which has not already been taken.

me.uk

Was the first new SLD to be introduced since we started operating the .uk Registry in 1996 and is intended for use by individuals as personal domains.

net.uk

This is a restricted SLD domain that is for Internet Service Providers. Anyone wishing to register a net.uk SLD must pass a test as outlined in the Rules for the Registration and Use of Domain Names. For this reason net.uk domains take longer to issue than the fully automated co.uk or org.uk domains.

org.uk

A fully open SLD, this is intended for non-commercial organisations and is most commonly used by charities, trades unions, political parties, community groups, educational councils, professional institutions and others.

plc.uk

In the same way as ltd.uk, this is a restricted SLD available only to registrants that are able to pass a test as outlined in the Rules for the Registration and Use of Domain Names. The restrictions are designed to work with the system used by Companies House, so companies should always be able to have a domain name which closely matches their company name and which has not already been taken.

sch.uk

This SLD is for schools. However, because many schools share similar if not identical names, geographical areas are used as third level domains to differentiate between them. For example: schoolname.area.sch.uk.

The second level domains we delegate management of include:

ac.uk

This is for academic establishments such as universities and is managed by JANET (UK).

gov.uk

This is for government bodies and is managed by JANET (UK).

mod.uk and mil.uk

These are for UK Armed Forces and Ministry of Defence establishments and systems. The domain management may be contacted via hostmaster@mod.uk.

nhs.uk

This is for NHS organisations. The domain management may be contacted via dnsteam@nhs.net.

police.uk

This is for the UK’s police forces and applications are approved by the College of Policing.