When a link in Wikipedia leads to nowhere, it is displayed in red to alert our editors that it requires attention. A red link can mean one of two things:
The link is broken and no longer leads to an article (perhaps because the underlying article was deleted). In such a case, the link needs to be removed or renamed to point to an existing article.
A new article is needed. When a Wikipedian writes an article, it is common practice to linkify key topics pertinent to an understanding of the subject, even if those topics don't have an article on Wikipedia yet. This has two applications:
From within an article, such a link prepares the article to be fully supported. At any time, a Wikipedian may independently write an article on the linked-to subject, and when this happens, there's already a link ready and waiting for it. The red link also gives readers the opportunity to click on it to create the needed article on the spot.
In topic lists, it is useful to include every topic on the subject you can possibly find or think of. When they are turned into links, the list immediately shows where the gaps in Wikipedia's coverage for that subject are, since all of the topics missing articles will show up in red. Such lists are useful tools in developing subject areas on Wikipedia, as they show where work is needed most.
