Most people think that when they do a keyword search, the computer searches everything: an entire website, the complete text of an article, or every word in a book.
In fact, the search is usually limited to specific parts of the record in order to increase the relevance of your results and speed of the search. These parts are called fields. The whole system is based on the assumption that if your keyword appears in an important field, like the title of an article, that article is more likely to be relevant to you than another article where your keyword appears once in just a footnote.
It can be useful to find out what fields a database searches automatically. Here is a list of some possible fields a database may search: