Five by five by extension has come to mean "I understand you perfectly" in situations other than radio communication, the way Loud and Clear entered slang, post-WW2.
It is sometimes used as slang term to mean "everything is good". The character "Faith" from the "Buffy The Vampire" TV series used it this way.
Sometimes also used in athletic training.
Or, as slang:
A person would ask; "How are you doing?" The responder could say; "I'm 5 x 5." (5 by 5, meaning I'm doing/feeling great.)