Affiche vs. poster
The French words affiche and poster both mean poster in English, but they have subtle differences in usage and connotation.
Affiche
A2Affiche is the traditional French word for poster. It is more commonly used and has a broader range of applications in French.
Il y a une affiche du nouveau film sur le mur.
(There's a poster of the new movie on the wall.)
Les affiches électorales sont partout dans la ville.
(Election posters are everywhere in the city.)
J'ai acheté une belle affiche d'art pour ma chambre.
(I bought a beautiful art poster for my room.)
Poster
B1Poster is a more recent borrowing from English. It's less frequently used and often refers specifically to decorative or pop culture posters.
Elle a un poster de son groupe préféré sur la porte.
(She has a poster of her favorite band on the door.)
Les adolescents aiment décorer leurs chambres avec des posters.
(Teenagers like to decorate their rooms with posters.)
J'ai trouvé un vieux poster de cinéma dans le grenier.
(I found an old movie poster in the attic.)
Summary
While affiche is the more versatile and commonly used term for all types of posters in French, poster is often associated with decorative or pop culture images. Affiche can be used in formal and informal contexts, whereas poster is more casual and specific to certain types of posters.