The Domain Name System maps hostnames to Internet address using a hierarchical namespace where each level in the hierarchy contributes one component to the FQDN. For example, the computer foldoc.doc.ic.ac.uk is in the doc.ic.ac.uk domain, which is in the ic.ac.uk domain, which is in the ac.uk domain, which is in the uk top-level domain.
5. <programming> A specific phase of the software life cycle in which a developer works. Domains define developers' and users' areas of responsibility and the scope of possible relationships between products.