When you view all spaces, you may notice a listing of 'Space Categories' along the left-hand side of the page:
The space categories are set by space administrators individually to 'tag' their space with relevant labels. This is more similar to a tag cloud of spaces rather than a strict category listing. Chances are your space will not be included within a category.
To add or edit space categories, you must be a space administrator.
Select Space Tools > Overview and select Edit next to the Space Categories listing