Backup and recovery deals with concepts, procedures, and strategies that are needed to protect a database against data loss.
Such data loss can be caused by media failure or user errors.
A media failure occurs when it is not possible anymore to read or write a file, typically because of disk head crashes.
User errors seem to be way more common: someone accidentally dropps a table or performs bad DML statements.
Some sources even state that user errors are the greates single cause of database downtime.
A backup is basically a copy of the data that is stored in the database and the necessary metadata (such as configuration files) that are needed to run and operate the database.
Recovery encompasses all steps that are needed to reconstruct an operating database after a media failure (or user error).
A well planed backup and recovery strategy enables to return a corrupted database to desired state with minimum impact and minimum DBA effort.