Every document in every library database is indexed to capture individual bits of information about the document. For example, its title, author, publication year, publisher, etc. These bits of information are recorded in fields.
The default field in a database is usually 'All Fields' or 'Anywhere'. Searching this field means that you're searching all fields at the same time. Other common fields include Author, Title, Source / Journal Name (=journal title), Abstract, and topical fields (such as Keywords, Subjects, and Descriptors).
Databases sometimes use abbreviations for fields, for example SU - Subjects, AU - Author, or TI - Article Title. These abbreviations are called 'field codes'.
Field searching is searching in a specific field of database records. It's particularly helpful when, for instance,
Nearly all databases have an Advanced Search page with Boolean drop-downs and multiple fields to choose from. This way of searching is called 'guided searching'.
Suppose you have been assigned to read articles by Tilburg University professor Bovenberg on fiscal policy. Your course lecturer has advised you to search for useful articles on this topic in the renowned Journal of Public Economics. She has also suggested you use the library database EconLit.
The example below shows how efficient a field search can be.
A simultaneous search in the Author, Subjects, and Source field (=the field to use for journal titles in EconLit) -- using the Boolean operator AND ➊ -- returns 4 articles written by professor Bovenberg on fiscal policy, published in Journal of Public Economics.