Five by five is the best of 25 possible subjective responses used to describe the quality of communications. "Five by five" (occasionally written "'5 by 5", "five-by-five", "5 x 5", or "5-by-5"), by extension, has come to mean "I understand you perfectly" in situations other than radio communication. A further shortened form is "five by". Post-World War II, the phrase "Loud and Clear" entered common usage with a similar meaning.