A general overview article is one that combines summarized content from many specialized articles into one broadly-scoped article. E.g., the general overview article United States contains sections summarizing content contained in history of the United States, geography of the United States, politics of the United States, etc. General overview articles can be useful when it would be impractical to put all the information about a subject in a single article, due to article length and/or readability concerns.
General overview articles also can be useful for addressing bias and undue weight concerns, while still providing readers with an easy way to access information on fringe opinions. For instance, the Holocaust article does not contain extensive content about Holocaust denial, since Holocaust denial theories are fringe opinions that must not be given undue weight. It does not even provide wikilinks to a variety of articles on different Holocaust denial theories, as a large number of such links would also give those opinions undue weight. Instead, the article contains a link to Holocaust denial, a general overview article that contains links to more narrowly-scoped articles such as Did Six Million Really Die? and Denying the Holocaust.
A general overview article need not always merely take the form of a parent article. It can also take a subset of information, relevant to a certain narrowly-scoped subject matter, from many different articles and combine it into one place for easy reference by the reader. For instance, list of countries that regulate the immigration of felons is both more narrow and more broad than immigration in Australia, immigration in New Zealand, etc. It is broader in that it covers more than one country. It is narrower in that it covers only the immigration of felons. But it still might be considered a general overview article in that its scope is wider than, say, an article on Australian law concerning immigration of felons, which might cover the history of Australia's prohibition against felons immigration, the politics surrounding the prohibition, case law concerning the prohibition, etc.
General overview articles are better than disambiguation pages in which clearly one meaning is of primary importance/usefulness/interest. Even if the general overview articles starts out in poor quality, the increase in its visibility by replacing the disambiguation page with it may spur improvements in its quality.
Useful general overview articles are not to be deleted per criterion for speedy deletion A10 as being duplicative of existing content.