A miniature portrait? Dollhouse decor? Painted figurines? A Persian miniature?
A Russian lacquer box? They are all miniature art.
In western art history, a progression is accepted from illuminated manuscripts to miniature portraiture, and on to today's contemporary miniature revival.
The term "Miniature" as applied to the miniature portaits most popular from the 17th to 19th centuries, actually comes from the Latin term minium, meaning the red lead pigments prominently used in illuminated manuscripts. (To color with minium was the Latin verb miniare, conjugated to the past participle of miniatus, which became the Italian term for the art of illuminating a manuscript, miniatura.)
It's not just size that matters. The common feature of miniature art is the fine detailing. There is so much attention to detail in a good miniature that it can only be fully appreciated under magnification, where more will be revealed than can be seen with the naked eye.
In my painting "Ponte Vechio" you can actually see into some of the windows and archways of Florence, though many of these portals are smaller than a letter on this page.