Valve's newest update to their Steam system for games is a feature called Steam Tags. This update will allow users - not just the developers behind games and apps - the ability to tag games and apps. This update is still in Beta mode, but is live for the public now.
Users will be able to access tags for content through the Steam Store, tagging where they deem it appropriate. According to Valve, "tags that are applied frequently will become featured categories." Users will be able to tag games with anything - you're literally typing in these tags as you go. You'll find this Steam Tags interface first and foremost on games in the Steam Store with "View and edit tags for this game".
Steam is already organized by popular tags - this link leads to "Action." Users have already begun adding tags like "Comic Book" to the store for titles like LEGO Batman and Scribblenauts. A new bit of exploration power will be added to the "For You" tab in Steam with this update as well, with tags recommended for you based on a variety of criteria like tags you apply most often.
"Q. Can I tag a product with any word?
A. Yes, the system is intended to support a broad variety of concepts, genres, and attributes. The tag you apply may not appear to other users until enough other people have applied the same tag to that product." - Valve
Tags are able to be viewed in every language Steam is available in, and you'll be able to add tags in your chosen language just as easily as accessing them in the tags listing. This tagging feature also adds filtering to the mix - narrowing your searches by tags until you pinpoint a game or app of your choice.