What does it mean to say that one attribute of a table is functionally dependent on another?

When we say that one attribute of a table is functionally dependent on another, it means that the value of the first attribute is determined by the value of the second attribute. In formal terms, if attribute A functionally determines attribute B, then for every unique value of A, there is exactly one corresponding value of B. This relationship is crucial in database design as it helps to ensure data integrity and reduce redundancy by organizing data in a way that reflects these dependencies.