I guess in parts of the world where narrow guage is uncommon people would call it "miniature".   Here in the northeastern United States, where narrow guage is practically non-existant, the only non-standard guage track can be found on "miniature" trains in amusement parks and the like.   Technically, I guess they would be narrow guage since the engines and cars are really full-size, although they are made to resemble their standard gauge cousins!