In programming, a namespace is a set of names with their specifications (definitions or declarations). This is pretty ambiguous so their use describes them better than what they are — namespaces are used because many things may share the same name across files and libraries. When we collect names into a namespace, we have it such that no two items in the same name space can share the same name.
If we only use one namespace in a given file, we can specify this. In C++, we can use:
using namespace std // swap out std for a namespace ID