What is the difference between Categories, Keywords, Labels and Tags?

Question

Is there a standard way of using Categories, Keywords and Tags in the context of blogs, websites and web applications? I am not sure if it is a case of these being equivalent of synonyms in some cases, but I don't recall seeing keywords and tags used together. Also, in terms of usage, it is not common to see the word categories used because these are normally specific to the type of blog or website, whereas keywords and tags seem to be used in a more generic sense. I have also seen the word Label used in a similar way.

I would like to know whether these terms have specific meaning or relate to specific parts of the website content and user interface design. It seems like these terms are concepts for physical and logical grouping of content.

Some suggestions are that there can be fixed (categories) versus user generated (tags), or broad groupings (categories, labels) versus specific groupings (keywords, tags).

Answer 1

In the context of a blog:

Categories
Categories are predefined and there should not be too many of them. Their use is closer to a folder system where a blog post gets put in one or more folders. They should be visible and easily accessible because they form the secondary organizing principle for the blog (primary being chronology).
E.g. a post about the iPhone 5 on a blog that also covers laptops, tablets and other smartphones, could be filed under the categories "smartphone" and "apple".

Labels and Tags
The idea of "tagging" something is synonymous with "labeling": you put labels on something and all them together describe what it is or what it is about. While re-using tags is encouraged to keep the amount of different-but-similar tags from exploding, tags can usually be created on the fly without restrictions. Because they're not defined they support a more loose and free organization based on association. Tags are presented in or next to a blog post, to link to other posts with the same tag. Tags don't do well as a structural feature, but it's not uncommon to show a tag cloud or list of most popular tags.
E.g. a post about the iPhone 5 could be tagged with "news", "iPhone", "iPhone5", "smartphone", "iOS" and "apple".

Keywords
Keywords generally do the same thing as tags and labels do, but it is not also a verb ("keywording"?). Keywords on the web are also already used for something else than what tags are used for: they sit in the head of a document to describe (primarily to search engines) what the document is about. Therefore they are not interactive and cannot be used by users to find blog posts about specific subjects.

Answer 2

Categories and Tags are UI tools and their use depends upon your need and context. In a project, I have used Tags in replacement of Categories where mental model was making it hard for the categories to be seen as "containers" or "sections" and Tags did the job well.

I don't think there is any different in keywords and tags unless you are using these terms in developer sense. Tags could be graphical in nature while keywords are primarily text elements, but for the user, they are pretty much the same.

Answer 3

Just opinion but I have done document management for a while

A category is more of a classification like animal, vegetable, mineral.
There is a right right answer to classification.

A tag is looser and it may change over time. For example Urgent. But is is a structured list (enumeration). But an admin would control the possible tag values.

To me keywords is even looser. It is a structured list but end users can addkeywords on the fly. Or it is not even a structured list as all. It is just individual search terms a user can add on the fly. Like a search engine will pick up keywords and index them.