In very simplistic terms it was a sports car built by Matra/Simca, supported by the French government to win Le Mans, which it did 3 years running from 1972 to 1974. Built to the 3.0L sports car regulations after the FIA outlawed the 917 and 512 it was built with the sole intention of winning the 24 hours but it did go on to compete in other rounds of the World Sports Car Championship into the mid 70's. The engine was also used in F1 by Liger and Matra iteself if I remeber correctly. These were effectively the cars that came before Group C.
A simple summary and lots more to it but effectively French specials!