Liquid Template Variables - current tags
From Spiffy Stores Knowledge Base
The current_tags of a collection are the tags that have been used to filter the current view of the collection.
For example, with the URL:
/page /collections/hair_raising_stuff/lime+electric+unforgettable
In this case, current_tags will be "lime,electric,unforgettable".
There may be additional tags which can be accessed using collection.tags.