Descriptive linguistics is a general term for the activity of describing the structures of particular languages.
Descriptive linguistics is sometimes contrasted with theoretical linguistics, but it would seem that the better contrast is with general linguistics. Descriptive linguistics is devoted to the description of particular languages (with more or less theoretical sophistication, but never atheoretically), and general linguistics studies language in general.
The term apparently originated in the 1930s in North America. An influential early textbook was Gleason (1955).
French linguistque descriptive
German deskriptive Linguistik