Constructed languages can still have "native" speakers, if children learn it at a young age from parents who have learned the language; there are estimated to be 200-2000 native speakers of Esperanto, for example.
2. Sometimes any language used by human beings (be it naturally evolved like English, or constructed like Esperanto) is considered a "natural" language, while programming languages and data representation languages for computers are classed as artificial. This usage can be seen in the term natural language processing.