What does "QRM" refer to in radio communication?

In the context of radio communication, "QRM" stands for unwanted interference from other radio transmitters. This term is part of the Q-code, a standardized set of abbreviations used by amateur radio operators and professionals alike to simplify communication. QRM specifically indicates the presence of interference that affects the quality of the received signal.

When radio waves are transmitted, various factors can lead to interference, such as overlapping frequencies from nearby stations, atmospheric conditions, or even electrical noise from devices. Recognizing QRM is essential for operators to troubleshoot and manage their transmissions effectively. Understanding this term can help radio operators identify and mitigate interference issues, ensuring clearer communication.

The other options provided do not accurately describe what QRM signifies in radio communication, as they either reference nonexistent concepts or unrelated forms of modulation.