1. What does it mean?
사녹 shortens 사전 녹화, advance recording. In idol fandom it commonly means a music-show performance recorded before broadcast, or attending that recording as an audience member.
Also written or said as 사전녹화, sanok
2. The nuance
Recording and broadcast dates can differ. Audience entry, repeated takes, and start times depend on the actual production; 사녹 does not mean the performance is necessarily live on television.
3. Examples
“사녹은 아침인데 방송은 저녁에 나와.”
The recording is in the morning, but the broadcast airs in the evening.
“사녹 참여 전에 집합 시간을 다시 확인했어.”
Before attending the pre-recording, I checked the meeting time again.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.