When you tell a reporter something off the record, it means they promise not to use that information in any news story they report. Sometimes the juiciest stuff is said off the record!
Since the early twentieth century, off the record has been used to describe anything said to a reporter in confidence. Just uttering the phrase, "This is off the record" during an interview should be enough to keep anything else you say from appearing in print, or being recorded. You can tell your friend something is off the record if you want her to keep it to herself — it's confidential, just between the two of you.