Stub
A "stub" is an article that does not contain much information. If you see this notice on a page, it usually means that the wiki community would like for the article to be expanded (have more information added to it).
Overview
Articles on wikis are meant to cover as much information as they can about the subject of the page. A stub constains only a very basic description, and/or is missing most of the information, and so it should be expanded upon.
In cases where the subject has little information, such as articles about an item that only has the stats/where it can be obtained, if it's a common occurrence in the game (or other topic) it's recommended a custom ambox for this wiki, that can be called something like Template:Low info.
Pages that are not articles, such as Templates, Categories, or Redirects are not meant to contain information, thus cannot be stubs.
Expanding articles
To get a page to stop being a stub, it is best to begin by expanding upon the little information already written. For example, say that you have a page of a location that only cointains where in the map is located. You can expand upon it by also noting what other locations are nearby.
You can also improve it by adding new information. In the example, you could expand it by adding who lives in there, if it has any notable places, etc.
It is also recommended to add relevant internal links. It is best to link pages that are important to understand the article. Different wikis have different conventions on how many times a link should be added. For example, it can be added in every data table (including infoboxes), and the first time it's mentioned in the main content.