One of the terms (etc.) in this wiki

There is a template for term definitions, used in the namespace “t”.

I'm using any of these words interchangeably as covering the names of concepts and the names of categories.

The point here is that there is no sharp distinction between these concepts.

• A tag is usually taken as any word or phrase that a writer (typically of blogs) thinks of as having a significant connection with a post. I tend not to use the word myself, as it is sometimes used in opposition to having a more orderly, agreed category scheme. The point about agreeing these schemes is that greatly facilitates collaboration. Personally I tend not to use the word ‘tag’, because of its association with unstructured folksonomies.
• A theme tends to be a topic of particular interest which the writer writing a series about, or a term that keeps coming up in several posts.
• A topic is something that a writer takes as significant, in a way that it is the main subject of at least one post.
• People tend to use the word term more neutrally or formally, which is why I have chosen it as the actual name of this page, and for terms which I give definitions of in this section.

My own meaning covers any word or phrase I want to define or clarify, explain my usage if it is not completely standard, or write about because I take it to be significant. I will try to link from any significant uses of the term, so that anyone (including me) can cross-refer.