By one denotes the category which is the homotopy category of Top with respect to weak equivalences given
either by homotopy equivalences – .
or by weak homotopy equivalences – .
Depending on context here Top contains all topological spaces or is some subcategory of nice topological spaces.
The study of was the motivating example of homotopy theory. Often is called the homotopy category.
The simplicial localization of Top at the weak homotopy equivalences yields the (∞,1)-category of ∞-groupoids/homotopy types.
Let now denote concretely the category of compactly generated weakly Hausdorff spaces. And Let be the subcategory on CW-complexes. We have .
There is a functor
that sends each topological space to a weakly homotopy equivalent CW-complex.
By the homotopy hypothesis-theorem is equivalent for instance to the homotopy category of the standard model structure on simplicial sets.
The category can be studied by testing its objects with objects from . This is the topic of shape theory.