“Artwork on paper” means exactly that;- prints, watercolours, acrylics on paper, etchings, aquatints, mezzotints, engravings, book-plates, pencil drawings, etc; the most important common factor being that it will need protection from the environment, normally by glazing.
The glass is normally prevented from touching the surface of the artwork by either a mount, see below, or by a wooden spacer or inner frame. The spacer itself needs an acid-free tape on the reverse, to protect the paper from the acid in the wood.
A mount is so much more than a spacer – it can completely enhance or spoil your picture. It needs to be the right colour, the right width, and to be of conservation quality. It can even give the wrong time-frame to a picture – since double mounts are a relatively recent trend, a Victorian watercolour would look strange in the simple double mount which looks fine on a Mary Ann Rogers. And a strong colour would be even worse. It’s a little like seeing the jet trails across the sky in a John Wayne spaghetti western.