Two species are known as Japanese maple, Acer japonicum and Acer palmatum, and there are dozens of species of both. There are also dozens more species of Acer. I’ve got at least 6, ranging from one which is nearly 2m wide but not much above knee height , which is currently brilliant red, to one which is twice the height of my neighbour’s house, with wonderful green and white striped bark.
So when you’re thinking of buying one, google the variety name to see what you’re getting.