In a keyword search, items will come up whenever those words are found in a title, abstract, description, or subject. The word may be a minor part of the items that are found because the keyword search does not consider relevance. Usually, the items with the most keywords will come up first on the list, but this does not necessarily mean that those are the best items for your research.
There are times when you are doing research for a new or less well-known topic and a keyword search may be your only option. However, if you are getting hundreds or thousands of hits, you should refine the search.
When searching by subject, it means that the person creating the index has determined that the subject is an important part of the work. In general, subject searching will produce more high quality results.
