1. What does it mean?
노맛 combines English no with 맛, taste. It is a short negative judgment that food does not taste good to the speaker, rather than a technical description of its ingredients.
Also written or said as nomat
2. The nuance
It can sound rude, especially to the person who prepared the food. It does not specifically mean low-sodium, bland, unsafe, or spoiled; those are separate descriptions.
3. Examples
“내가 소스를 잘못 넣어서 이번 요리는 노맛이야.”
I added the wrong sauce, so this attempt doesn't taste good.
“노맛이라고만 하지 말고 어떤 점이 아쉬운지 말해 줘.”
Instead of just saying it tastes bad, tell me what could be better.
Sources
References support the meaning and usage. Example sentences are written for NoCapWiki.