What is the difference between “books”, “articles”, and “issues”?

In the past, while working for TVP Magazine, we released issues made of articles. But we then focused more on articles, separating them from issues, so that people can easily find them. We also made several articles that merged into books. So, it was confusing. Now we call everything “books”. We do not release issues anymore containing a few articles, but we release articles directly as books.