 A subject heading is a word or phrase that is assigned to an article or other resource and describes the topic of the resource. It's a bit like a social media hashtag, but without the hash symbol. You might be thinking, isn't that a keyword? Subject headings and keywords are both types of terms you use to search, but there's a difference. Keywords are the words you choose that describe the key ideas you're searching for. Subject headings use a controlled vocabulary, meaning there's a list of possible headings and the relevant subject headings are assigned to each article. A single article might have multiple subject headings, especially if it covers a range of topics. Searching by subject heading is more powerful than searching by keyword. Here's why. When you search by keyword, that word might show up in a number of places in relation to the article, such as the abstract, the author's name, the journal's title, and other fields, even if it's not specifically what the article is about. This means your search results may include many articles that are not relevant to you when you search by keyword. When you search by subject heading, you're limiting your results to articles that are actually about that topic. Keep in mind that not every concept has a subject heading, so in some cases you won't be able to find a subject heading that means exactly what you're looking for. Rather than trying to convert every keyword into a subject heading, it's often best to use a combination of keywords and subject headings when searching. Subject headings are also useful because they are arranged in the hierarchy of broader and narrower terms. This is sometimes called a tree structure because the narrower terms branch out from the broader terms. Searching the tree may give you ideas for search terms you hadn't considered. For example, if you search nurse-patient ratio as a subject heading and don't find many results, you could find the broader term, personnel staffing and scheduling, and try that one instead. Part of that tree would look like this in the CINNL database. Different databases use different subject heading systems. For example, CINNL uses CINNL subject headings, while a lot of other databases, such as PubMed, Medline and Cochrane, use a system called Mesh. This means you'll need to look up your subject headings in each database you use. We hope this helps. Thanks for watching.