As a rule, names in a namespace cannot have more than one meaning, that is, two or more things cannot share the same name. A namespace is also called a context, as the valid meaning of a name can change depending on what namespace applies. Names in it can represent objects as well as concepts.

Each language is a namespace, whether it is a natural or ethnic language, a constructed language, the technical terminology of a profession, a dialect, a sociolect, or an artificial language (e.g., a programming language).

For many programming languages, a namespace is a context for identifiers

See WIKIPEDIA for further definition http://en.wikipedia.org/wiki/Namespace