Tag! You're it! Tag is a playground game in which you try to catch other players. A tag is also a label or marker that provides some information about the thing it's attached to, like the tag inside the neck of your sweater.
Items for sale often display price tags, and people at a social event sometimes wear name tags. You can also use tag as a verb to mean "to mark with a tag." This word has many colloquial meanings too, including "nickname" and "identifying graffiti mark." There's also the verb meaning "to touch another player in a game of tag."