In a database, each document is described in a record or citation. Each citation consists of a number of individual parts called fields. You can search for the information stored in many of these field.
(In Modules 3 and 4 you will see this record and field structure in more detail.)
When you search by a field, the computer will "look" only in that field when it looks through all the records in the database. It will try to match your search term.
For example . . .
Author Search looks only in the author field.
Title Search looks only in the title field.
Subject Search looks only in the subject heading field.
Date Search looks only in the date field.
But . . . a Keyword Search matches your search term anywhere in the record. It is the broadest search.