A noise budget is the amount of error that an encrypted computation can accumulate before the ciphertext becomes too noisy to decrypt correctly. In homomorphic encryption, every addition or multiplication increases noise a little. The system works only while that noise stays below a safe threshold, so the budget is a practical limit on how complex an encrypted workload can be.
In cyber security, noise budget matters because it determines whether privacy-preserving computation remains reliable. If parameters are chosen badly, or a model uses too many operations, the output can degrade into garbage even though the data stayed encrypted. Defenders manage this by selecting conservative encryption parameters, reducing circuit depth, and benchmarking real workloads. Attackers may try to abuse excessive computation as a denial-of-service pressure point or exploit weak parameter choices that make encrypted processing unstable.