A 3-Manifold is a 3-dimensional space that ...
- (Wikipedia, 2015) ⇒ http://en.wikipedia.org/wiki/3-manifold Retrieved:2015-2-7.
- In mathematics, a 3-manifold is a space that locally looks like Euclidean 3-dimensional space. Intuitively, a 3-manifold can be thought of as a possible shape of the universe. Just like a sphere looks like a plane to a small enough observer, all 3-manifolds look like our universe does to a small enough observer. This is made more precise in the definition below.