A notion derived by abstraction from our sense impressions.
It is conceived as a medium constituted by extra posed parts in which our perceptions of bodies are localized.
In so far as there are really existing bodies possessing quantity and hence extension, space may be regarded as real, but as an abstraction it is ideal, in the mind.
Such space is uncurved and tri-dimensional, i.e., Euclidian space.
Mathematical space may have more than three dimensions and may be curved, either elliptic or hyperbolic.
According to Einstein the real space of the world is curved, and hence the physical universe must be finite.
New Catholic Dictionary