A dialect continuum means a large geographical area, where the spoken language differs only slightly from village to village, but over a longer distance the differences become that huge, that mutual intelegibility is not possible, which would indicate, that these dialects are Abstandsprachen (pl. of Abstandsprache). But these dialects can be seen as dialects of a single language, as long as if there is a common standard language, through which communication is possible. Such a situation is called Diglossia.
The Romance languages of Portugal, Spain, France and Italy are often cited as an example of this, although the intermediate dialects are tending toward extinction.