Posters mean a less expensive option for the buyer. They are 'quantity, not quality' based. That doesn't necessarily mean you can't get a good result, as far as crisp clean detailed image w/perfect coloration, though. I have some excellent posters of my own work!
Some sites offer them in either matte or glossy, as well. I've offered both posters & prints for years and heard no complaints about either. Btw, just because it's an art print or a giclee, printed with archival inks on higher quality paper, doesn't mean it always going to 'look' better image-wise. I've seen some pretty washed out prints and some posters with perfect detail & coloring!
So, yes, there IS a difference between a print & a poster. However, here, I think they may mean the same thing? Not sure...or sure 'why' that would be? It's kind of confusing.
But, posters give those on a the smallest budget a chance to 'own' a piece of your work. I've yet to hear a mention re fading with any I've sold. Maybe it's because they have taken precautions re protective glass or location of in home or office?
In any event, life is short...and options are available, which is a good thing for both artist & patron, whatever their pocketbook & desires dictate!