What is a stub?
When creating or editing a Tricki article, one may mark it as a stub by ticking a checkbox on the edit form. Our working definition of a stub is that it is an article with no substantial mathematical content and with no links forward to any articles with substantial mathematical content. (That is, a parent of a non-stub is always a non-stub.) The thought behind this is that there are two directed graphs of interest on the Tricki: one with all articles, whether written or unwritten, and the other the set of all ancestors of articles with interesting content. The stub feature allows one to explore either of these trees with ease, because if an article is marked as a stub, then all links to that article are clearly marked as well, with a little leaf symbol .
Stub articles vs incomplete articles
One may also mark articles as incomplete, as discussed on the editorial markup page. The difference between a stub article and an incomplete article is that an incomplete article may very well contain interesting content while still being far from complete, whereas a stub is essentially guaranteed not to lead you to interesting information.