Final answer:
A predicate identifies the conditions that must be met for a row to appear in the query results. It is used in the WHERE clause of an SQL statement to filter rows based on a logical expression.
Step-by-step explanation:
The blank in the question should be filled with the term predicate. A predicate identifies what must exist or a requirement that must be met before a row is included in the results of a query. In database management systems, the predicate is a logical expression that is used to filter rows in a table. For example, if a student wants to find all the books in a library database that were published after the year 2000, the predicate would be something like 'year_published > 2000', which would filter out all the books published before 2001. This criterion is often specified in the WHERE clause of an SQL (Structured Query Language) statement. To ensure a query returns the correct information, it is crucial that the predicate accurately reflects the desired conditions for selection.