"Ligne claire (French for "clear line") is a style of drawing pioneered by Hergé, the Belgian creator of The Adventures of Tintin. It is a style of drawing which uses clear strong lines which have the same thickness and importance, rather than being used to emphasize certain objects or be used for shading (for this reason it is sometimes also called the democracy of lines). Additionally, the style often features strong colours and a combination of cartoonish characters against a realistic background. The use of shadows is sparse and all elements of a panel are delineated with clear black lines.....The Ligne claire style achieved its highest popularity in the 1950s, but its influence started to wane in the 1960s and was seen as old fashioned by the new generation of comic book artists...."
Above is a panel from Herge's The Adventures of Tintin.