From latin territorĭum, the territory is the portion of land belonging to a city, a province, a region, a country, etc. The concept is also used to mention the location (ground, space) that an organization or that a person controls or owns.
National, on the other hand, is an adjective that describes what belongs or which is linked to a nation (constituent sovereignty of a State or the human community whose members share common cultural characteristics).
The concept of national territory therefore concerns the portion of surface that belongs to a particular country and on which a State exercises sovereignty. This is not only a space of Earth but also air and sea space if the country in question has sides.
The national territory is divided into several sub - national entities. These administrative and political divisions typically have a local authority which, in one way or another, meet the national administration.
A city, a municipality and a region are examples of sub - national entities within a national territory. The level of autonomy of these divisions depends on the legislation of each country.
In Spain, for example, the territory is divided into autonomous communities. These communities are nations (like Catalonia and the Basque country) which are part of a unit (Spain) but have their own culture and their own language. The autonomous communities and other sub-national entities tend to become independent of the national State and, therefore, no longer to be part of the national territory of the country to itself as free States.