Almost every search we do online is a KEYWORD search.
This means search results will have your search term anywhere on the page. This is why you often get all kinds of unrelated results in a web search. Search engines don't group pages by subject, and aren't smart enough to know when you type "achilles" you mean the tendon and not the hero of myth, or vice versa. Searches would even return items written by John A. Achilles, or companies named 'Achilles'. Keywords hit on the string of characters you type, not the meaning.
Library resources, however, are organized by SUBJECT.
Every item in the library catalog or in a library database has been assigned specific Subject Terms. This means all the resources about Achilles the hero of myth are grouped and searchable together, under a different heading than resources about the tendon. Subject terms can be a more efficient way to search since they reflect meaning, but subject terms themselves are not always obvious or intuitive.
Not sure when to search with keywords, and when to search with subjects? Use this Quick Guide:
Finding Reference Sources:
Finding articles:
We know most searches for information start on Google. It's important to remember though, that Google's results are ranked by popularity, not necessarily authority. The best source for your information might not be in the first 20, or even the first 100 results. To help narrow your results from the start: