As a <user> I want <to be able to browse segments by category> so that <I can easily narrow down videos>.

We currently have the idea of tags that will be beneficial for searching algorithms and for users who want to browse tags to find videos, however it could also be beneficial to have a hierarchical category structure so that users can drill down a path of categories to find videos on a topic.

For example, at the top of the hierarchy all the videos could be defined as either `theory` (left brained) or `application` right brained, and down the tree the categories would go from very general to more specific.

I see two possibilities for this:

1) each video is assigned a category or
2) each tag is assigned a category.

We will also need to define how categories will be created and what will be the mechanism for assigning tags or videos to a category.

Update:

Thinking more, we could even have "category types" so that we could create different sets of hierarchies/trees. For example, the `theory/application` tree could have the category type of `Approach` and there could also be a `Difficulty` category type that would include `beginner/intermediate/advanced`.

Some categories and category types could be "curated" and others could be added by users.