What are "related tags"?

When submitting content you can add up to 20 tags per content item. Those tags that have been used together to tag an item are all related. Example, if you tag an item with "gear" and "biner" and you tag another item with "gear", "rack" and "shoes" then when looking at the "gear" you will see related tags "biner, rack, shoes" - all the tags that has ever been used with "gear".