What are the concepts of "langue" and "parole"?

The concepts were elaborated by the Swiss linguist
Ferdinand de Saussure during his courses on general linguistics at the University of
Geneva from 1907 to 1911. Saussure died in 1912, but the notes of his course were
published posthumously in 1916 as Cours de Linguistique Générale.
The concepts of "langue" and "parole" are part of his effort to shift the
study of linguistics from a predominantly diachronic to a synchronic paradigm. The
diachronic approach had focused mainly on historical changes in languages, while
Saussure tried to understand how a linguistic system works. The "langue" is the social
dimension of language and is formed by the general linguistic conventions
(grammar rules, syntax) that we all share in a given language. The "parole" represents
the single utterances that individuals create.