If your database suffers a problem at 3:22 p.m. and your backup was taken at 4:00 a.m. you're probably hoping there is a way to recover the changes made between those two times. What you need is known as Point-in-Time Recovery (PITR).
Regrettably, if you've made a backup with the pg_dump utility at 4:00 a.m., then you won't be able to recover to any other time. As a result, the term PITR has become synonymous with the physical backup and restore technique in PostgreSQL.