Documents in Lexis and Westlaw are divided into individual sections, known as fields or segments. This allows you to search only for words that appear in the specified fields. For example, if you want to search for opinions by a specific judge, you search for the judge's name in the Judge field, and you will only get cases where that judge wrote the opinion, rather than other cases where the judge's name might appear elsewhere in the opinion.
The fields available in each database vary depending on the type of content and the database. See the documents below for detailed information on which fields are available for which types of content in which database. When you are signed into either Lexis or Westlaw, you can also select the content type (e.g., Cases) and then click on the Advanced Search link to get a guided form with the fields available for that content type.