It is possible to tag (a text label) any content, including folders. This service provides an API for creating, deleting, and adding tags, and other tag management methods.
Tags are simple text labels that are attached to a piece of content. Each piece of content can have multiple tags. Folders also have a TagScope object which encapsulates information about the tags used on content in that folder. The TagScope object contains an array that lists Tags in count order. There are methods to find out how many times a particular tag is used.
Get tags applied to node: List<String> tags = serviceRegistry.getTaggingService().getTags(nodeRef);