Publication is making a content available to the general public.
A journal article, or book, is called a publication. A conference paper, or working paper, is in principle a publication. Sometimes, a conference paper may get cited many times. A piece of ‘scientific information’ posted on a blog can be seen as a ‘publication’ (in this sense, you can publish everyday!)
But peer reviewed journal articles are always preferred to other forms.
A list of publications is often a requirement to applying for academic positions.
Once published, the content is not always available to the public. Users have to pay a fee in order to download an article. Many people discontent with that. They initiate ‘free access’, ‘open’ web-based stores in order to make a publication really ‘public’.
This can be an example. Second example, the one that contains several hundreds of books from various sources. The second example is here. The third is here. I strongly recommend the second.
