It's a small ornament or object that is decorative. It's a French phrase that has been borrowed directly into English (we do that sometimes). Here are a couple of definitions and explanations: http://en.wikipedia.org/wiki/Objet_d'art http://www.thefreedictionary.com/objet+d'art http://www.merriam-webster.com/dictionary/objet%20d'art

I would translate by "pieces of art", it' just something that is considered artistic like a painting, a sculpting.

It's a French word. Where did you learn it? In English, it would be 'objects of art', but I'm not sure how it's being used because you didn't give any context.