Five by five

[Kit]

[Five by five] is a radio communications expression that means loud and clear. One of the fives represents the S units of reception strength. The other five is a rating of the signal clarity. Five by five is a good, clear signal. The radio use of this expression goes back to the 1950s: All right, testing, one-two-three-four. . . Five by five, Mr. Holloran! (Hunter, [Blackboard] Jungle, 1954).
The more metaphorical meaning, popularized by [Faith Lehane] from the television show Buffy the Vampire Slayer, wasnt recorded until the 1980s.
The use of the word is primarily used in the military, or when discussing something similar.