- noun an alteration in the usual condition of something
- noun a change in an ecosystem caused by an alteration of the environmental conditions, by a process such as drought, pollution or felling of woodland
- noun something that upsets the normal condition of something
- An undesired interference, interruption, or variation in a condition, quantity, or process. For instance, noise which interferes with the transmission or reception of a signal.
- In a control system, an unwanted control signal.
- noun a noise or movement of people which annoys other people