What is a gallery? A museum?
It is, of course, easiest to explain in art terms, but the concept may be applied to all media.
A gallery is a group of images that are all linked to from one page. This page usually has thumbnails to help you select which image you wish to view at full size. A museum contains links to many galleries. These links may or may not have thumbnails. Often the links on museum pages are just text descriptions of the gallery.
Again, this concept does not necessarily apply exclusively to art. For music, the gallery may be the works of one musician, and a museum may be links to many different musicians. Or a gallery could be one album of that musician and a museum could be links to every album of that musician.