"Chanson" is the French word for "song." "Un chanson," as spoken in the French language, could refer to any piece of music, although in English usage, the word usually refers to a particular kind of melodic French music. Popularized in the Middle Ages and Renaissance, a chanson typically tells an epic tale with themes of heroism, religion, love, and sacrifice.
There are a number of different kinds of chansons, including Chanson Courtoise, Burgundian Chanson, Parisian Chanson, and, perhaps most well known, Chanson de Geste. Le Chanson de Roland, or Song of Roland, is the most famous of these. It is a tragic tale of war in the time of Charlemagne, and is often studied academically as the earliest surviving work of French literature.