Idealization
Every thing has more than one property. It is specified in multiple ways, interacting with many other things.
In the sciences this multitude is often considered disturbing. It makes the things incalculable, unpredictable in their behavior.
Scientific theory always covers only a — partial — aspect of the real things. These therefore appear as idealized things in theory, reduced to what is essential — in that context.
But also on their practical side, sciences normally need to preclude disturbing influences. This is done by spaces which are closed exactly in this sense, thus providing a context that fits the theory.