5 by 5

5 by 5 Five by five is an expression used in aviation (and maybe other) 

radio communication to indicate the quality and loudness of received voice 

transmissions. Rated one to five indicates - first figure - clearness and - 

second - loudness. Five by five means that a transmission is received clear 

and loud (in clear words usually loud and clear is used...). One by one, on 

the other hand, means it can hardly be heard and is not understandable. If 

you have a loud but distorted transmission, you may hear two by five, and a 

weak but clearly understandable one may be called five by three... The 

definition of this must be included somewhere in a radiotelephony document 

of ICAO (International Civil Aviation Organisation)