Here is an example of tags from another program:
It is a feature of os x I think (sorry I'm not a developer). But the point is to have a flexible way to assign labels to individuals cards so that they can be easily sorted in multiple ways by selecting the tags rather than assigning cards to a single exclusive folder. It makes grouping cards easier (for example, you could have a card tagged with "animals" and "french" and filter for only the cards that meet both criteria.
Does this make sense?
, 12 months