In the early days of radio, hams used Morse code to communicate over radio. The speed of sending Morse code, like the speed of a typist, depends on the skill of the operator. Typical Morse speeds might be around 13-20 words a minute. Having to send a commonly used phrase like “Can you change frequency to 14.020 Mhz?” takes a lot of time to send at those speeds. To speed up the flow of a conversation (QSO), radio operators invented a short hand system of three letter codes, called Q-Codes. The sample above can then be reduced to QSY 14.020? QSY Meaning change frequency. Q-codes can be used as an instruction or as a question. QST 14.202 is an instruction whereas QSY 14.020? Is a question.

There are a lot more  Q-Codes defined, than are used commonly. A short list of some common Q-Codes with informal definitions are:

QRM – Interference from another signal (i.e. man made interference)

QRP – Running low power, typically under 5 watts.

QRZ – Who are you?, please identify

QSB – Signal is fading in and out. i.e. band conditions are changing.

QSL – Can you confirm?  Confirmed.

QSO – A conversation between operators.

QST – A Bulletin.  Also the name of the ARRL magazine publication.

QSY – Change frequency

QTH – Location. Where are you?

A full list of Q-Codes is available here.