It honestly depends because there's so many situations where the term lowpoly specifies a different threshold on the polycount of a model.
In terms of film industry speak lowpoly could be used as the term for a production ready model that has been converted from a model that has millions of polys, made from NURBS, or non-implicit surfaces.
In terms of the game industry in game production low poly is the version of a model that has been baked down from a high poly source that is used in the game. I prefer the term "game poly" since I think it communicates the idea across better and using that instead of low poly would help alleviate the cluttered number of meanings low poly already has.
In terms of an artstyle low poly means literally a model that uses as few triangles (tris) as possible, typically the sweatspot for the amount of triangles used is under 1,000 tris. Generally when it comes to appeal a model that uses as little tris as possible coupled with the lowest resolution necessary while still carrying across a clear and strong design is considering more technically impressive because the art comes from the optimization, mastery, and creative use of limited resources that's a call back to the days of the PS1, N64, and Saturn days of early 3D video game graphics.
One last thing is that there's another definition that low poly (a fake kind of low poly or "faux" low poly) has kind of like in video games but usually more commonly seen in film and abstract art. The style of low poly is more like a kind of minimalism kind of like those 3D renderings of abstract landscapes even though the amount of triangles might actually be pretty high the idea is to create abstraction though simple shapes to create a kind of minimalist or impressionist style seen in fine art.