Wikipedia stands on its sources: scientific articles and monographs, but also news media and online content. In fact, the number of news media and online content sources in Wikipedia is considerably larger than scientific ones. When considering Wikipedia as a source of altmetric data, this broader context of use becomes relevant. We provide a breakdown of Wikipedia sources by typology and an overview of how they are used in Wikipedia. We find that scientific sources are especially important in STEM Wikipedia, while news media sources find broader applicability. We also assess the reliability of news media sources in Wikipedia, finding that it is overall high. When news media sources are used in STEM Wikipedia, their selection for reliability is the strictest across Wikipedia.