This is a cloche. Cloche means bell in French. I believe a cloche was originally referred to as a small glass dome used to force plants to bloom (like a mini green house). But in decor terms, it's usually a display (raised on a stand) under glass.
DIY Miniature Winter Wonderland terrarium: Turn a glass vase into a miniature winter wonderland. Directions: Arrange sheet moss in the bottom of a vase and top with bottle brush trees, holly and ornaments of your choice. Dust with fake snow.