?.... i take it you meant ,what is a SEO friendly article?
It means optimising for the search engines, not stuffing your articles with top Google search terms, and targeting a search term such as 'how to write SEO articles'. For that example, it should be in the Title, 1st and last paragraph, and signature -no more.
Its also a lot to do with content structure, where to use tags like bold and links, and in such a way so that you write for humans while keeping the article SEO optimised for your target Google terms. Read up on keyword research and i suggest you also look at keyword density, i can see lots of hubs here on writing SEO articles.